Grease composition and rolling apparatus

ABSTRACT

A grease composition is produced by mixing a thickener comprising a fluoro resin and a second thickener component (a metallic soap, a complex metallic soap, an N-substituted terephthalamic acid metal salt, organic bentonite or a calcium sulfonate complex) into a base oil. This grease composition is excellent in heat resistance, load carrying capacity, water resistance, rust protection, lubricating life and the like. A rolling apparatus filled with the above grease composition has excellent lubricating ability and is long-lived under high-temperature conditions. Moreover, a grease composition is produced by mixing a thickener comprising a fluoro resin and carbon black as a second thickener component into a base oil. This grease composition is excellent in heat resistance, water resistance, rust protection, lubricating life, electric conductivity and the like. A rolling apparatus filled with the above grease composition has excellent electric conductivity and is long-lived under high-temperature conditions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of patent application Ser. No.10/378,060, filed Mar. 4, 2003, the entire disclosure of which isincorporated herein by reference. Priority is claimed based on JapanesePatent Application Nos. 2002-062069, filed Mar. 7, 2002; 2002-073110,filed Mar. 15, 2002; 2002-252665, filed Aug. 30, 2002; and 2002-286026,filed Sep. 30, 2002.

FIELD OF THE INVENTION

The present invention relates to a grease composition, which hardlydisperses and has excellent high-temperature performance. Moreover, thepresent invention relates to a rolling apparatus, which has low torqueand excellent acoustic performance and generates a few dusts, and inparticular, the present invention relates to a rolling apparatus, whichis preferably used in electronic intelligence equipment, semiconductormanufacturing machines and others.

Furthermore, the present invention relates to a grease compositionhaving excellent lubricating ability and heat resistance. Still further,the present invention relates to a rolling apparatus, which hasexcellent lubricating ability and is long-lived under high-temperatureconditions, and in particular, it relates to a rolling apparatus, whichis preferably used as a rolling or sliding portion of machines usedunder high-temperature and high-speed conditions including carelectrical components such as alternators or electromagnetic clutches;auxiliary equipment for car engine such as idler pulleys; and businessmachines such as copying machines or printers.

Furthermore, the present invention relates to a grease compositionhaving excellent rust protection, extreme-pressure property, waterresistance and lubricating life, and a rolling apparatus which islong-lived although it is used under stringent conditions.

Furthermore, the present invention relates to a grease compositionhaving excellent heat resistance, lubricating ability and rustprotection. Still further, the present invention relates to a rollingapparatus which has excellent lubricating ability and is long-livedunder high-temperature conditions, and it particularly relates to arolling bearing, which is preferably used in electrical machines for acar engine which are required for heat resistance, load carryingcapacity and durability.

Furthermore, the present invention relates to a grease compositionhaving excellent lubricating ability and electric conductivity. Stillfurther, the present invention relates to a rolling apparatus, which hasexcellent electric conductivity and is long-lived under high-temperatureconditions, and in particular, it relates to a rolling apparatus, whichis preferably used as a rolling or sliding portion of machines usedunder high-temperature and high-speed conditions including carelectrical components such as alternators or electromagnetic clutches;auxiliary equipment for car engine such as idler pulleys; and businessmachines such as copying machines or printers.

DESCRIPTION OF THE RELATED ART

(1) A rolling apparatuses (e.g. rolling bearings, linear guideapparatuses, ball screws, etc.), which are used in electronicintelligence equipment such as a hard disk drive (hereinafter referredto as HDD) or laser beam printer (LBP), semiconductor manufacturingmachines and others, are required to have various performances such thatthese apparatuses generate a few dusts, have low torque and excellentacoustic performance, and are long-lived.

Moreover, with the development of high-precision electronic intelligenceequipment and semiconductors in recent years, the use conditions(temperature, speed, etc.) of rolling apparatuses, which are used inelectronic intelligence equipment and semiconductor manufacturingmachines, have become increasingly strict. Under such strict useconditions, the above stated various types of performance are requiredto be excellent.

For example, in the case of electronic intelligence equipment such asHDD used under a clean atmosphere, if a gaseous oil or the fineparticles of grease are released from the inside of a bearing when arolling apparatus rotates, the fine particles pollute a recording mediumor the like and cause operation errors. Therefore, it is most importantto suppress the amount of dusts generated.

As a grease composition enclosed in such a rolling bearing for HDD,Undock C (Trade name), which is a grease comprising a mineral oil as abase oil and a sodium complex soap as a thickener, is well known, andthis product has been used over 20 years because it causes a smallamount of dusts.

When excellent performance of low torque and low noise is required, agrease comprising a lithium soap as a thickener and an ester oil as abase oil has been used at times.

Moreover, Japanese Patent Laid-Open No. 2000-109874 discloses a fluorogrease composition obtained by mixing a silicone oil into a fluorogrease consisting of a fluoro oil and a thickener. This fluoro greasecomposition has a property such that oil does not leak so much from thegrease.

Furthermore, Japanese Patent Laid-Open No. 2001-187892 discloses agrease composition comprising a silicone oil as a base oil,polytetrafluoroethylene as a thickener, silica aerogel and anextreme-pressure additive. This grease composition has a property suchthat it has excellent low-temperature flow property, wear resistance,heat resistance and low torque property at a low temperature.

However, in the above sodium complex soap-mineral oil grease, thedispersibility of the thickener is insufficient and so it hardly becomeshomogenous, and thereby problems regarding acoustic and vibrationperformances occur in the early stage of rotation of the rollingbearing. In addition, since this grease has strong hygroscopicity andgets hard over time, and thereby the flow property in the rollingbearing decreases, this grease also has a problem of causinginsufficient lubrication and readily generating abnormal sounds from thecage.

Therefore, when excellent performance of low torque and low noise isrequired, the above described lithium soap-ester oil grease has beenused at times. However, since this grease easily disperses (causes alarge amount of dusts), there is a great risk that the grease mightpollute a recording medium or the like when it is used in a rollingbearing for HDD. Moreover, since the temperature used for the rollingbearing for HDD is more and more increased, the above described lithiumsoap-ester oil grease cannot be applied in some cases.

Further, the grease compositions as disclosed above in Japanese PatentLaid-Open Nos. 2000-109874 and 2001-187892 comprise a very expensivesilicone oil or fluoro oil, these grease compositions are expensive whencompared with common greases.

SUMMARY OF THE INVENTION

Thus, it is a first object of the present invention to solve the abovedescribed problems of the prior art techniques and to provide a greasecomposition which is hardly dispersed and has excellent high-temperatureperformance. Moreover, it is also the first object of the presentinvention to provide a rolling apparatus, which has low torque andexcellent acoustic performance, and generates a few dusts.

(2) Cars (passenger cars) tend to be directed towards downsizing, weightsaving and the expansion of the living space, and therefore cars areforced to reduce their engine room space. For this reason, thedownsizing and weight saving of electrical components or auxiliaryequipment for car engine are increasingly progressing. In addition, carsare required for silence improvement, the hermeticity of the engine roomis progressing, and thereby the temperature in the engine room becomeshigher. Accordingly, the above described components or equipment forcars are also required for high-temperature resistance property. Forexample, bearings for electrical fan motors had previously been used ata bearing temperature of 130° C. to 150° C., but in recent years, thesame bearings have been required to resist a high temperature of 180° C.to 200° C.

As described in Japanese Patent Publication No. 2977624, bearings usedunder high-temperature environment of 150° C. or higher have previouslybeen dealt with by filling the inside of the bearing with a greaseobtained by mixing a lithium soap and a urea compound into a syntheticoil type lubricating oil. However, under a high-temperature condition of160° C. or higher, even this grease generates seizure in an early stage,and so a grease having further higher heat resistance is required.

On the other hand, in OA machines, especially in copying machines or thelike, since color fine particles (toner) consisting of a thermoplasticresin and a coloring agent is fused by heating and then fixed on a paperby pressure, a heater is inserted into the axis of a roller, andtherefore the temperature of the rolling bearing of a bearing portionsometimes rises to 140° C. to 200° C., depending on the models.Therefore, for such rolling bearings, a grease having excellent heatresistance should be used.

For example, a fluoro grease comprising polytetrafluoroethylene (PTFE)as a thickener and a perfluoropolyether oil (PFPE oil) as a base oil hasexcellent heat resistance, and so a rolling bearing filled with thisfluoro grease can be used under high-temperature environment of 160° C.or higher.

However, since it is difficult to add additives that can be mixed intocommon greases into the above described fluoro greases, these greasesare likely to have poor lubricating ability, rust protection and ametallic corrosion preventing property. Moreover, the fluoro greaseshave another disadvantage in that these greases are more expensive thansynthetic oil type greases by approximately 5 to 20 times.

Japanese Patent Laid-Open No. 11-181465 describes a grease composition,heat resistance of which is improved by blending a fluoro oil with aurea grease. However, since a mineral oil or synthetic oil that is abase oil of the urea grease has a poor affinity for a fluoro oil, theabove grease composition has a high oil separation percentage, andtherefore this grease composition has a disadvantage in that the use ofthe grease composition is inappropriate for a bearing used in componentswhich rotate at a high speed.

Thus, it is a second object of the present invention to solve the abovedescribed problems of the prior art techniques and to provide a greasecomposition having excellent lubricating ability and heat resistance.Moreover, it is also the second object of the present invention toprovide a rolling apparatus, which has excellent lubricating ability andis long-lived under high-temperature conditions.

(3) With the development of mechanical technology in recent years,mechanical devices tend to be directed towards downsizing, weight savingand high-speed rotation. Mechanical portions such as a bearing and agear become increasingly exposed at a high temperature. Therefore, insuch mechanical portions, a grease used at a high temperature is used.Moreover, a grease used at a high temperature is used also for bearingswhich are used under high-temperature conditions, such as bearingintegrated into iron manufacturing machines (e.g. continuous castingmachines, rolling mill for iron and steel, etc.,) various heatprocessing apparatus or driers.

Examples of such a high-temperature grease include a metallic soapgrease which uses, as a thickener, a metallic soap such as Ca, Al, orLi, and a complex metallic soap; an organic grease which uses an organiccompound such as polyurea, a terephthalamic acid metal salt or a fluororesin; and an inorganic grease which uses an inorganic compound such asbentonite.

However, each of these greases also has a disadvantage. For example, themetallic soap grease such as an alminum complex grease has excellentlubricating ability, but it cannot maintain the grease structure for along time under high-temperature conditions. The grease comprisingpolyurea is likely to cause hardening phenomenon, and the greasecomprising a terephthalamic acid metal salt has large oil separation.Further, the grease comprising bentonite has insufficient rustprotection, extreme-pressure property and water resistance.

As a grease which solves the above problems, a grease obtained by addingdibasic acid esthers into organic bentonite to enhance rust protectionis known (Japanese Patent Laid-Open No. 6-200273). There is also known agrease obtained by adding the metal salt of carboxylic acid with asubstitution at condensed ring into organic bentonite to enhance ametallic corrosion preventing property (Japanese Patent Publication No.2711150).

However, the grease described in the above Patent Publication still hasa problem regarding insufficient extreme-pressure property and waterresistance.

Thus, it is a third object of the present invention to solve the abovedescribed problems of the prior art techniques and to provide a greasecomposition having excellent rust protection, extreme-pressure property,water resistance and lubricating life. Moreover, it is also the thirdobject of the present invention to provide a rolling apparatus, which islong-lived although it is used under strict conditions.

(4) As stated above, with the development of mechanical technology inrecent years, mechanical devices tend to be directed towards downsizing,weight saving and high-speed rotation, and rolling bearings used inelectrical machines surrounding a car engine also tend to have a hightemperature. On the other hand, resources and power saving efforts arerequired, and maintenance-free mechanical devices are also required.Accordingly, rolling bearings are required not only for heat resistancebut also for reliability and durability.

Presently, in rolling bearings used under high-temperature environmentover 180° C., a fluoro grease, clay mineral grease or the like isgenerally charged. However, although these greases are excellent in heatresistance, they have a disadvantage in that they have poor lubricatingability, load carrying capacity and rust protection.

As a grease satisfying conditions such as rust protection, heatresistance and load carrying capacity, a calcium sulfonate complexgrease which comprises, as a thickener, a calcium sulfonate complexcontaining calcium carbonate is known (Japanese Patent Publication No.5-8760). However, when this calcium sulfonate complex grease is usedunder high-temperature conditions over 180° C., it does not have thesame level of heat resistance as a fluoro grease.

Thus, it is a fourth object of the present invention to solve the abovedescribed problems of the prior art techniques and to provide a greasecomposition having excellent heat resistance, lubricating ability andrust protection. Moreover, it is also the fourth object of the presentinvention to provide a rolling apparatus, which has heat resistance sothat it can be used under high-temperature conditions over 180° C., aswell as having excellent load carrying capacity, durability and rustprotection, and particularly to provide a rolling bearing which ispreferably used in electrical machines surrounding a car engine.

(5) Cars (passenger cars) tend to be directed towards downsizing, weightsaving and the expansion of the living space, and therefore cars areforced to reduce their engine room space. For this reason, thedownsizing and weight saving of electrical components or auxiliaryequipment for car engine are increasingly progressing. In addition, carsare required for silence improvement, the hermeticity of the engine roomis progressing, and thereby the temperature in the engine room becomeshigher. Accordingly, the above described components or equipment forcars are also required for high-temperature resistance property.

At present, as a grease composition used for the rolling bearing of eachof the above components, a grease composition comprising a synthetic oilas a base oil and a urea compound as a thickener is mainly used, andthis urea compound-synthetic oil grease has excellent lubricatingability up to a temperature of 170° C. to 180° C. However, under hightemperature conditions of 200° C. or higher, the evaporation of the baseoil, the hardening of the grease associated therewith, and the softeningof the grease by the construction of the thickener occur, and thereforethere is a risk that a rolling bearing filled with the ureacompound-synthetic oil grease might generate seizure in an early stage.

Moreover, as described in Japanese Patent Laid-Open No. 11-72120, in therolling bearing used in each of the above components, there are somecases where hydrogen generates by water present in the bearing, and thegenerated hydrogen enters in a bearing steel constituting an inner ring,an outer ring and rolling elements, thereby causing a flaking of formedwhite structure due to hydrogen brittleness. This is considered to occuras a result of the phenomenon that a direct electric current isgenerated by metallic contact by vibration or the like at a portionbetween the inner and outer rings which becomes isolated by the oil filmof a lubricant, and that hydrogen ions thereby generate from the waterpresent in the bearing. The generation of hydrogen and the flaking offormed white structure thereby can significantly be controlled by theimpartation of electric conductivity to a grease.

On the other hand, in OA machines, especially in copying machines or thelike, since color fine particles (toner) consisting of a thermoplasticresin and a coloring agent is fused by heating and then fixed on a paperby pressure, a heater is inserted into the axis of a roller, andtherefore the temperature of the rolling bearing of a bearing portionsometimes rises to 140° C. to 200° C., depending on the models.Therefore, for such rolling bearings, a grease having excellent heatresistance should be used.

Moreover, as described above, since the inner and outer rings of arolling bearing become isolated by the oil film of a lubricant, staticelectricity generates by rotation. Since the radiation noise has adverseeffects such as distortion on the copying screen of a copying machine,as described, for example, in Japanese Patent Publication No. 63-24038,there is taken a countermeasure of charging a grease with electricconductivity in a rolling bearing to electrify the portion between innerand outer rings, thereby eliminating static electricity.

For example, a fluoro grease comprising polytetrafluoroethylene (PTFE)as a thickener and a perfluoropolyether oil (PFPE oil) as a base oil hasexcellent heat resistance, and so a rolling bearing filled with thisfluoro grease can be used under high-temperature conditions of 180° C.or higher.

However, since it is difficult to add additives that can be mixed intocommon greases into the above described fluoro greases, these greasesare likely to have poor lubricating ability, rust protection and ametallic corrosion preventing property. Moreover, the fluoro greaseshave another disadvantage in that these greases are more expensive thansynthetic oil type greases by approximately 5 to 20 times.

Japanese Patent Laid-Open No. 11-181465 describes a grease composition,heat resistance of which is improved by blending a fluoro oil with aurea grease. However, since a mineral oil or synthetic oil that is abase oil of the urea grease has a poor affinity for a fluoro oil, theabove grease composition has a high oil separation percentage, andtherefore there is a disadvantage that the use of this greasecomposition is inappropriate for a bearing used in components whichrotate at a high speed.

Thus, it is a fifth object of the present invention to solve the abovedescribed problems of the prior art techniques and to provide a greasecomposition having excellent lubricating ability and electricconductivity. Moreover, it is also the fifth object of the presentinvention to provide a rolling apparatus, which has excellent electricconductivity and is long-lived under high-temperature conditions.

(6) As stated above, grease composition are classified into thefollowing 4 types according to the types of a thickener:

-   -   (i) a metallic soap grease comprising a metallic soap such as        Li, Ca, Na or Al;    -   (ii) a complex metallic soap grease comprising a complex        metallic soap such as Li, Ca, Na and Al;    -   (iii) an organic grease comprising an organic compound (an        organic thickener) such as polyurea, a terephthalamic acid metal        salt or a calcium sulfonate complex; and    -   (iv) an inorganic grease comprising an inorganic compound (an        inorganic thickener) such as bentonite or silica gel.

However, as described in the “Lubrication Control Manual Book” edited bythe Japan Lubricating Oil Society and the Lubrication Control DiffusionTask Force (the Japanese Lubricating Oil Society, published Mar. 20,1990) and “A Brief History of Lubricating Greases” written by Arthur T.Polishuk (Llewellyn & McKane, Inc., published 1998), it has previouslybeen thought that, when different types of grease compositions aremixed, the properties of the grease compositions are altered anddeteriorated in many cases. This deterioration naturally occurs when 2types from among the above 4 types of grease compositions are mixed, butit could also occur when 2 types of metallic soap greases are mixed, inwhich the type of metals is different.

When a significant deterioration occurs in a grease, the greasestructure is destroyed, significant softening of the grease or decreaseof the dropping point occurs, and the grease is liquefied at times.Moreover, there are also cases where additives which are added to agrease composition, act on one another and reduce the performance of thegrease composition. For these reasons, it has generally been believedthat the mixing of grease compositions should be prevented as much aspossible.

Grease compositions used in rolling apparatuses such as a rollingbearing, a ball screw, a linear guide apparatus and a linear bearing arerequired to have various performances such as lubricating performance,load carrying capacity, heat resistance, water resistance, low torqueand few dusts generating property. To obtain such a grease componenthaving many excellent performances, a method for mixing greasecomponents each having one of the above performances is considered to beeffective. However, probably because it has generally been believed thatthe mixing of grease components comprising different types of thickeneris not good, the above method has seldom been used.

A few examples include Japanese Patent Publication No. 6-31375disclosing the combined use of an N-substituted terephthalamic acidmetal salt and polyurea, Japanese Patent Laid-Open No. 7-268370 (& U.S.Pat. No. 5,948,737A) disclosing the combined use of a hydrogen-additiongrease and a fluoro grease or fluoro oil, and Japanese Patent Laid-OpenNo. 2001-3074 disclosing the combined use of a sodium soap and a lithiumsoap.

Although two types of thickener are used in combination, if theexcellent performances of both thickener consist with each other, theabove described grease component having many excellent performances canbe obtained. Thus, the present invention adopts a method involving thecombined use of two different types of thickener to achieve the abovedescribed first to fifth objects.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

(1) The grease composition of the present invention is a greasecomposition in which two different types of thickeners are used incombination, and the grease composition of the present invention hasmany excellent performances. A large number of combinations of two typesof thickeners can be conceived, but in the present invention, as a firstthickener, a fluoro resin is used. That is to say, the greasecomposition of the present invention is a grease composition comprisinga base oil and a thickener, wherein the above thickener consists of afluoro resin and a second thickener component.

As described later, as the second thickener component, a metallic soap,a complex metallic soap, an N-substituted terephthalamic acid metalsalt, organic bentonite, a calcium sulfonate complex or carbon black isused.

It should be noted that a different type of a third thickener may alsobe used in combination to such an extent that it does not impair thepurpose of the present invention.

(2) To achieve the above first object, the present invention has thefollowing features. That is to say, the grease composition of thepresent invention comprises a metallic soap as the above secondthickener component.

Since this grease composition comprises both a fluoro resin and ametallic soap as a thickener, it hardly disperses and has excellenthigh-temperature performance. Moreover, this grease composition impartsexcellent acoustic performance and torque performance to a rollingapparatus in which the grease composition is enclosed.

The above thickener preferably comprises 10 to 80% by mass of the fluororesin and 90 to 20% by mass of the metallic soap.

If the composition of the thickener is out of the above range, there isa risk that the grease composition might generate an increased amount ofdusts or have insufficient high-temperature performance. Moreover, thereis also another risk that when the grease composition is charged in arolling apparatus, the acoustic performance of the rolling apparatusmight decrease, or torque might increase.

In order to decrease the amount of dusts generated from the greasecomposition and to enhance the high-temperature performance so as toenhance the acoustic performance and torque performance of a rollingapparatus in which the grease composition is enclosed, the thickenermore preferably comprises 20 to 70% by mass of the fluoro resin and 80to 30% by mass of the metallic soap.

Furthermore, the content of the above described thickener is preferably10 to 33% by mass based on the total mass of the composition.

If the content of the thickener is less than 10% by mass, the greasecomposition becomes too soft and thereby the amount of dust generatedincreases, and if the content is more than 33% by mass, the greasecomposition gets so hardened that it becomes difficult for the greasecomposition to exert sufficient lubricating ability, resulting in a riskof decreasing acoustic durability. Taking into consideration the amountof dusts generated, acoustic durability and worked penetration, thecontent of the thickener is more preferably 15 to 30% by mass based onthe total mass of the composition.

The above base oil preferably comprises 20 to 70% by mass of aperfluoropolyether oil and 80 to 30% by mass of at least one of either amineral oil or synthetic oil.

Since the grease composition of the present invention comprises theperfluoropolyether oil as a base oil and the fluoro resin as athickener, it has excellent high-temperature performance. Accordingly, arolling apparatus in which the grease composition of the presentinvention is enclosed is long-lived under high-temperature conditions.Moreover, since the viscosity of the base oil of the grease compositionis controlled at low, the grease composition is also excellent inlow-temperature flow property.

The grease composition described in Examples 1 to 4 of Japanese PatentLaid-Open No. 7-268370 contains a small amount of fluoro oil, the samehigh-temperature performance as in the present invention cannot beobtained.

Moreover, since the grease composition of the present inventioncomprises, as a base oil, at least one of either the mineral oil orsynthetic oil, various additives can be added thereto, thereby impartingvarious performances such as lubricating ability, rust protection and ametallic corrosion preventing property to the grease composition.Furthermore, since the grease composition comprises, as a base oil, atleast one of either the mineral oil or synthetic oil, the greasecomposition of the present invention is low-priced when compared withthe conventional grease compositions comprising a silicone oil or fluorooil as a base oil.

If the content of at least one of either the mineral oil or syntheticoil is less than 30% by mass, there is a risk of not obtainingsufficient additive effects when additives are added to the greasecomposition. Moreover, when the content of at least one of either themineral oil or synthetic oil is less than 30% by mass, the content ofthe perfluoropolyether oil exceeds 70% by mass, and the greasecomposition thereby becomes expensive. In contrast, if the content of atleast one of either the mineral oil or synthetic oil exceeds 80% by massand that of the perfluoropolyether oil is less than 20% by mass, thegrease composition has insufficient high-temperature performance.

Moreover, it is preferable that the above perfluoropolyether oil has akinematic viscosity at 40° C. of 20 to 400 mm²/s, and at least one ofeither the above mineral oil or synthetic oil has a kinematic viscosityat 40° C. of 50 to 500 mm²/s.

If the kinematic viscosity at 40° C. of each of the above compoundsexceeds the above upper limit, there is a risk that the low-temperatureflow property of the grease composition might be insufficient and thatabnormal sounds might be generated when the rolling apparatus isactivated at a low temperature. To the contrary, if the kinematicviscosity of each of the above compounds is less than the above lowerlimit, it is not appropriate in terms of evaporation loss or lubricatingability. That is, if the viscosity of a base oil is too low, it becomesdifficult to form lubricating oil film which is enough to preventmetallic contact between the raceway surface and the rolling elementswhen the bearing is rotated at a high temperature.

In order to reduce this problem wherever possible, it is more preferablethat the above perfluoropolyether oil has a kinematic viscosity at 40°C. of 30 to 200 mm²/s, and at least one of either the above mineral oilor synthetic oil has a kinematic viscosity at 40° C. of 70 to 400 mm²/s.

Furthermore, it is preferable that the grease composition of the presentinvention has a worked penetration of 190 to 250.

In order to suppress dusts generated from a rolling apparatus in whichthe grease composition is enclosed, it is preferable to harden thegrease composition. However, if the grease composition is too hard, theflow property in the rolling apparatus decreases, resulting ininsufficient lubrication and then ready generation of abnormal soundsfrom a cage. Therefore, the worked penetration of the grease compositionis preferably 190 to 250. If the worked penetration is less than 190,the grease composition is so hard that the rolling apparatus filled withthe grease composition has decreased acoustic and torque performances.If the worked penetration exceeds 250, the amount of dusts generatedfrom the rolling apparatus increases.

Still further, the rolling apparatus of the present invention directedtowards achieving the above first object is a rolling apparatuscomprising an inner member having a raceway surface on the outersurface; an outer member which has a raceway surface opposed to theraceway surface of the inner member and is disposed outside of the innermember; and a plurality of rolling elements which are disposed betweenthe two raceway surfaces so as to flexibly roll therebetween, wherein aspace, which is formed between the inner member and the outer member andin which the rolling elements are disposed, is filled with the abovedescribed grease composition comprising a metallic soap as the secondthickener component.

Since the rolling apparatus with the above configuration is filled witha grease composition comprising both a fluoro resin and a metallic soapas thickeners, the rolling apparatus has low torque and excellentacoustic performance, generating a small amount of dusts.

Moreover, a grease composition comprising a complex metallic soap as theabove second thickener component can also achieve the above firstobject. That is to say, the grease composition of the present inventioncomprises a complex metallic soap as the above second thickenercomponent.

Since this grease composition comprises both a fluoro resin and acomplex metallic soap as thickeners, it hardly disperses and hasexcellent high-temperature performance. Moreover, this greasecomposition imparts excellent acoustic performance and torqueperformance to a rolling apparatus in which the grease composition isenclosed. The grease composition comprising the complex metallic soap asthe second thickener component has high-temperature performance moreexcellent than the grease composition comprising the metallic soap asthe second thickener component. However, regarding acoustic performance,the grease composition comprising the metallic soap as the secondthickener component is more excellent than the grease compositioncomprising the complex metallic soap as the second thickener component.

Moreover, a rolling apparatus filled with this grease composition canachieve the above first object. That is to say, the rolling apparatus ofthe present invention comprises an inner member having a raceway surfaceon the outer surface; an outer member which has a raceway surfaceopposed to the raceway surface of the inner member and is disposedoutside of the inner member; and a plurality of rolling elements whichare disposed between the two raceway surfaces so as to flexibly rolltherebetween, wherein a space, which is fomied between the inner memberand the outer member and in which the rolling elements are disposed, isfilled with the above described grease composition comprising a complexmetallic soap as the second thickener component.

(3) To achieve the above second object, the present invention has thefollowing features. That is to say, the grease composition of thepresent invention comprises an N-substituted terephthalamic acid metalsalt as the above second thickener component.

The above base oil preferably comprises a perfluoropolyether oil and atleast one of either a mineral oil or synthetic oil.

Since the grease composition of the present invention comprises theperfluoropolyether oil as a base oil and a fluoro resin as a thickener,it has excellent heat resistance. Moreover, since the viscosity of thebase oil is controlled at low, the grease composition is also excellentin low-temperature flow property. Furthermore, since the greasecomposition comprises, as a base oil, at least one of either the mineraloil or synthetic oil, various additives can be added thereto.Accordingly, the grease composition of the present invention isexcellent in lubricating ability, rust protection and a metalliccorrosion preventing property.

Further, since the grease composition comprises at least one of eitherthe mineral oil or synthetic oil as a base oil, and the N-substitutedterephthalamic acid metal salt as a thickener, the grease composition ofthe present invention is low-priced when compared with fluoro greases.

Still further, the above thickener preferably comprises 40 to 80% bymass of the fluoro resin and 60 to 20% by mass of the N-substitutedterephthalamic acid metal salt.

When the content of the N-substituted terephthalamic acid metal salt isless than 20% by mass and the content of the fluoro resin exceeds 80% bymass, it results in the high cost of the grease composition. To thecontrary, when the content of the N-substituted terephthalamic acidmetal salt exceeds 60% by mass and the content of the fluoro resin isless than 40% by mass, the heat resistance of the grease composition isinsufficient. In order to reduce this problem wherever possible, it ismore preferable that the thickener comprises 50 to 70% by mass of thefluoro resin and 50 to 30% by mass of the N-substituted terephthalamicacid metal salt.

Moreover, the above base oil preferably comprises 10 to 90% by mass ofthe perfluoropolyether oil and 90 to 10% by mass of at least one ofeither the mineral oil or synthetic oil.

If the content of at least one of either the mineral oil or syntheticoil is less than 10% by mass, sufficient additive effects cannot beobtained when additives are added to the grease composition. If thecontent of at least one of either the mineral oil or synthetic oil isless than 10% by mass, the content of the perfluoropolyether oil exceeds90% by mass, thereby resulting in the high cost of the greasecomposition. To the contrary, if the content of at least one of eitherthe mineral oil or synthetic oil exceeds 90% by mass and the content ofthe perfluoropolyether oil is less than 10% by mass, the heat resistanceof the grease composition is insufficient.

Moreover, the content of the above thickener is preferably 5 to 40% bymass based on the total mass of the composition.

If the content is less than 5% by mass, it becomes difficult to maintaina grease state, but if the content exceeds 40% by mass, the greasecomposition gets so hardened that it becomes difficult for the greasecomposition to exert sufficient lubricating ability.

Furthermore, it is preferable that the above perfluoropolyether oil hasa kinematic viscosity at 40° C. of 20 to 400 mm²/s, and at least one ofeither the above mineral oil or synthetic oil has a kinematic viscosityat 40° C. of 20 to 400 mm²/s.

If the kinematic viscosity at 40° C. of each of the above compoundsexceeds 400 mm²/s, oil film gets relatively thick and torque becomeslarge in a rolling apparatus filled with the grease composition of thepresent invention. Further, there is a risk that the low-temperatureflow property of the grease composition might be insufficient and thatabnormal sounds might be generated when the rolling apparatus isactivated at a low temperature. However, if the kinematic viscosity ofeach of the above compounds is less than 20 mm²/s, it is not appropriatein terms of evaporation loss or lubricating ability. That is, if theviscosity of the base oil is too low, it becomes difficult to formlubricating oil film which is enough to prevent metallic contact betweenthe raceway surface and the rolling elements when the bearing is rotatedat a high temperature.

In order to reduce this problem wherever possible, it is more preferablethat the kinematic viscosity at 40° C. of both parties is set at 30 to200 mm²/s.

Furthermore, the grease composition of the present invention comprisesadditives, and the content of the additives is preferably 20% or less bymass based on the total mass of the composition.

Further, the rolling apparatus of the present invention directed towardsachieving the above second object is a rolling apparatus comprising aninner member having a raceway surface on the outer surface; an outermember which has a raceway surface opposed to the raceway surface of theinner member and is disposed outside of the inner member; and aplurality of rolling elements which are disposed between the two racewaysurfaces so as to flexibly roll therebetween, wherein a space, which isformed between the inner member and the outer member and in which therolling elements are disposed, is filled with the above described greasecomposition comprising an N-substituted terephthalamic acid metal saltas the second thickener component.

Since the rolling apparatus with the above configuration is filled witha grease composition comprising both a fluoro resin and an N-substitutedterephthalamic acid metal salt as thickeners, it is long-lived underhigh-temperature conditions.

This rolling apparatus, especially a rolling bearing, can preferably beused in car electrical components, auxiliary equipment for car engine,or business machines used under high-speed and/or high-temperatureenvironment.

(4) To achieve the above third object, the present invention has thefollowing features. That is to say, the grease composition of thepresent invention comprises organic bentonite as the above secondthickener component.

Since this grease composition comprises the mixture of a fluoro resinand organic bentonite as a thickener, it has excellent rust protection,extreme-pressure property, water resistance and lubricating life.

The above thickener preferably comprises 5 to 95% by mass of the fluororesin and 95 to 5% by mass of the organic bentonite.

If the composition of the thickener is out of the above range, there isa risk that the rust protection or lubricating life of the greasecomposition might become insufficient. To ensure sufficient rustprotection or lubricating life, it is more preferable that the thickenercomprises 10 to 90% by mass of the fluoro resin and 90 to 10% by mass ofthe organic bentonite. Since the grease composition described inExamples 5 and 6 of Japanese Patent Laid-Open No. 7-268370 does notcontain a fluoro resin, the same rust protection or lubricating life asin the present invention cannot be obtained.

The content of the above thickener is preferably 3 to 40% by mass basedon the total mass of the composition.

If the content is less than 3% by mass, it becomes difficult to maintaina grease structure, but if the content exceeds 40% by mass, the greasecomposition gets so hardened that it becomes difficult for the greasecomposition to exert sufficient lubricating ability.

Moreover, the rolling apparatus of the present invention directedtowards achieving the above third object is a rolling apparatuscomprising an inner member having a raceway surface on the outersurface; an outer member which has a raceway surface opposed to theraceway surface of the inner member and is disposed outside of the innermember; and a plurality of rolling elements which are disposed betweenthe two raceway surfaces so as to flexibly roll therebetween, wherein aspace, which is formed between the inner member and the outer member andin which the rolling elements are disposed, is filled with the abovedescribed grease composition comprising organic bentonite as the secondthickener component.

The rolling apparatus with this configuration is long-lived, although itis used under stringent conditions.

(5) To achieve the above fourth object, the present invention has thefollowing features. That is to say, the grease composition of thepresent invention comprises a calcium sulfonate complex as the abovesecond thickener component.

Since this grease composition comprises both the fluoro resin and thecalcium sulfonate complex as thickeners, it has excellent heatresistance, lubricating ability and rust protection.

The above thickener preferably comprises 5 to 95% by mass of the fluororesin and 95 to 5% by mass of the calcium sulfonate complex.

If the composition of the thickener is out of the above range, there isa risk that the heat resistance, lubricating ability and rust protectionof the grease composition might become insufficient. In order to reducethis problem wherever possible, it is more preferable that the abovethickener comprises 10 to 90% by mass of the fluoro resin and 90 to 10%by mass of the calcium sulfonate complex.

Moreover, the content of the above thickener is preferably 10 to 40% bymass based on the total mass of the composition. If the content is lessthan 10% by mass, it becomes difficult to maintain a grease state, butif the content exceeds 40% by mass, the grease composition gets sohardened that it becomes difficult for the grease composition to exertsufficient lubricating ability.

Furthermore, the above base oil has a kinematic viscosity at 100° C. ofpreferably 3 to 60 mm²/s, and more preferably 5 to 40 mm²/s.

Still further, the rolling apparatus of the present invention directedtowards achieving the above fourth object is a rolling apparatuscomprising an inner member having a raceway surface on the outersurface; an outer member which has a raceway surface opposed to theraceway surface of the inner member and is disposed outside of the innermember; and a plurality of rolling elements which are disposed betweenthe two raceway surfaces so as to flexibly roll therebetween, wherein aspace, which is formed between the inner member and the outer member andin which the rolling elements are disposed, is filled with the abovedescribed grease composition comprising a calcium sulfonate complex asthe second thickener component.

The rolling apparatus with this configuration has heat resistance sothat it can be used under high-temperature environment over 180° C., andthe rolling apparatus also has excellent load carrying capacity,durability and rust protection. Among rolling apparatuses, a rollingbearing comprising a plurality of rolling elements which are disposedbetween an inner ring and an outer ring so as to flexibly rolltherebetween is particularly preferable.

(6) To achieve the above fifth object, the present invention has thefollowing features. That is to say, the grease composition of thepresent invention comprises carbon black as the above second thickenercomponent.

The above base oil preferably comprises a perfluoropolyether oil and atleast one of either a mineral oil or synthetic oil.

Since the grease composition of the present invention comprises theperfluoropolyether oil as a base oil and the fluoro resin as athickener, it has excellent heat resistance. Moreover, since theviscosity of the base oil of the grease composition is controlled atlow, the grease composition is also excellent in low-temperature flowproperty.

Moreover, since the grease composition of the present inventioncomprises carbon black as a thickener, it has excellent electricconductivity.

Furthermore, since the grease composition comprises, as a base oil, atleast one of either the mineral oil or synthetic oil, various additivescan be added thereto, and the grease composition is thereby excellent invarious performances such as lubricating ability, rust protection and ametallic corrosion preventing property.

Still further, since the grease composition comprises at least one ofeither the mineral oil or synthetic oil as a base oil and carbon blackas a thickener, the above grease composition is low-priced when comparedwith the conventional fluoro greases.

The above thickener of the grease composition of the present inventionpreferably comprises 40 to 80% by mass of the fluoro resin and 60 to 20%by mass of the carbon black. If the content of the carbon black is lessthan 20% by mass, the electric conductivity becomes insufficient. Whenthe content of the carbon black is less than 20% by mass, the content ofthe fluoro resin exceeds 80% by mass, resulting in the high cost of thegrease composition. To the contrary, if the content of the carbon blackexceeds 60% by mass and the content of the fluoro resin is less than 40%by mass, the heat resistance of the grease composition becomesinsufficient. In order to reduce this problem wherever possible, it ismore preferable that the thickener comprises 50 to 70% by mass of thefluoro resin and 50 to 30% by mass of the carbon black.

Moreover, the content of the above thickener is preferably 5 to 40% bymass based on the total mass of the composition. If the content is lessthan 5% by mass, it becomes difficult to maintain a grease state, but ifthe content exceeds 40% by mass, the grease composition gets so hardenedthat it becomes difficult for the grease composition to exert sufficientlubricating ability.

Furthermore, the above base oil of the grease composition of the presentinvention preferably comprises 10 to 90% by mass of theperfluoropolyether oil and 90 to 10% by mass of at least one of eitherthe mineral oil or synthetic oil.

If the content of at least one of either the mineral oil or syntheticoil is less than 10% by mass, the carbon black easily coagulates and soit does not become a grease state, and further, sufficient additiveeffects cannot be obtained when additives are added to the greasecomposition. Moreover, when the content of at least one of either themineral oil or synthetic oil is less than 10% by mass, the content ofthe perfluoropolyether oil exceeds 90% by mass, and the greasecomposition thereby becomes expensive. In contrast, if the content of atleast one of either the mineral oil or synthetic oil exceeds 90% by massand that of the perfluoropolyether oil is less than 10% by mass, thegrease composition has insufficient heat resistance.

Furthermore, it is preferable that the above perfluoropolyether oil hasa kinematic viscosity at 40° C. of 20 to 400 mm²/s, and at least one ofeither the above mineral oil or synthetic oil has a kinematic viscosityat 40° C. of 20 to 400 mm²/s. If the kinematic viscosity at 40° C. ofeach of both types of the above oils exceeds 400 mm²/s, oil film getsrelatively thick and electric resistance value increases in the rollingapparatus supplied with the grease composition of the present invention.Further, there is a risk that the low-temperature flow property of thegrease composition might become insufficient and that abnormal soundsmight be generated when the rolling apparatus is activated at a lowtemperature.

However, if the kinematic viscosity of each of the above compounds isless than 20 mm²/s, it is not appropriate in terms of evaporation lossor lubricating ability. That is, if the viscosity of the base oil is toolow, it becomes difficult to form lubricating oil film which is enoughto prevent metallic contact between the raceway surface and the rollingelements when the bearing is rotated at a high temperature.

In order to reduce this problem wherever possible, it is more preferablethat the kinematic viscosity at 40° C. of both base oils is set at 30 to200 mm²/s.

Moreover, it is preferable to set the DBP oil absorption of the abovecarbon black at 100 ml/100 g or more, the primary particle size at 100nm or shorter, and the specific surface area at 50 m²/g or larger.

Furthermore, the grease composition of the present invention comprisesadditives, and the content of the additives is preferably 20% or less bymass based on the total mass of the composition.

Still further, the rolling apparatus of the present invention directedtowards achieving the above fifth object is a rolling apparatuscomprising an inner member having a raceway surface on the outersurface; an outer member which has a raceway surface opposed to theraceway surface of the inner member and is disposed outside of the innermember; and a plurality of rolling elements which are disposed betweenthe two raceway surfaces so as to flexibly roll therebetween, wherein aspace, which is formed between the inner member and the outer member andin which the rolling elements are disposed, is filled with the abovedescribed grease composition comprising carbon black as the secondthickener component.

Since the rolling apparatus with this configuration is filled with thegrease composition comprising both the fluoro resin and the carbon blackas thickeners, it has excellent electric conductivity and is long livedunder high-temperature conditions.

This rolling apparatus, especially a rolling bearing, can preferably beused in car electrical components such as alternators andelectromagnetic clutches, or auxiliary equipment for car engine such asidler pulleys. Moreover, it can preferably be used also for businessmachines such as copying machines and printers.

(7) Examples of the rolling apparatus of the present invention directedtowards achieving the above described first to fifth object includesvarious apparatuses such as rolling bearings, ball screws, linear guideapparatuses and linear bearings.

The term “inner member” for the rolling apparatus of the presentinvention is used to mean a bearing inner ring when the rollingapparatus is a rolling bearing. Likewise, the term “inner member” isused to mean a screw shaft when the rolling apparatus is a ball screw, aguide rail when it is a linear guide apparatus, and a shaft when it is alinear bearing, respectively. The term “outer member” is used herein tomean a bearing outer ring when the rolling apparatus is a rollingbearing. Likewise, the term “outer member” is herein used to mean a nutwhen the rolling apparatus is a ball screw, a slider when it is a linearguide apparatus, and an outer casing when it is a linear bearing,respectively.

(8) Each of the components of the grease composition of the presentinvention will be explained below.

Fluoro Resin:

The type of the fluoro resin used as a thickener in the presentinvention is not particularly limited, and preferred examples includepolytetrafluoroethylene (PTFE); a copolymer of tetrafluoroethylene andanother ethylene unsaturated hydrocarbon monomer, the entire or a partof which is fluorinated (hereinafter referred to as atetrafluoroethylene copolymer); and others.

Examples of the tetrafluoroethylene copolymer include the following (1)to (4):

1) Denatured polytetrafluoroethylene obtained by copolymerizing one ormore types of comonomers selected from a group consisting ofperfluoroalkyl-trifluoroethylene ether, vinylidene fluoride,hexafluoroisobutene, chlorotrifluoroethylene and perfluoroalkylethylenes(e.g. perfluoropropene, etc.) with PTFE at a ratio of 0.01 to 3 mole %,and preferably 0.05 to 0.5 mole %.

(2) A tetrafluoroethylene (TFE) thermoplastic copolymer obtained bycopolymerizing at least one type of perfluoroalkylvinyl ether (whereinthe perfluoroalkyl group contains 1 to 6 carbon atoms) with TFE at aratio of 0.5 to 8 mole %. Examples of such a copolymer include acopolymer of perfluoropropylvinyl ether and TFE, a copolymer ofperfluoromethylvinyl ether and TFE, a copolymer of perfluoroethylvinylether and TFE, and others.

(3) A TFE thermoplastic copolymer obtained by copolymerizing perfluoroolefin containing 3 to 8 carbon atoms with TFE at a ratio of 2 to 20mole %. Examples of such a copolymer include a copolymer ofhexafluoropropene and TFE, and the like. Other comonomers having atrifluoroethylene ether structure may also be copolymerized with thiscopolymer, if the ratio is less than 5 mole %.(4) A TFE thermoplastic copolymer obtained by copolymerizingperfluoromethylvinyl ether (0.5 to 13 mole %) with one or more types ofmonomers of fluoride represented by the following formulas (I) to (III):

-   -   wherein R in formula (III) is a perfluoroalkyl group containing        1 to 5 carbon atoms and it is preferably CF₃. Each of X₁ and X₂        is independently a perfluoroalkyl group containing 1 to 3 carbon        atoms or F, and it is preferably CF₃.

Moreover, RF in Formulas (I) and (II) is at least one of the following(i), (ii) and (iii):

-   (i) a perfluoroalkyl group containing 2 to 12 carbon atoms,-   (ii) a compound having a chemical structure represented by the    following formula (IV), wherein r in the formula (IV) is an integer    of 1 to 4, and r′ is an integer of 0 to 3:    CF₂CF(CF₃)O    _(r)    CF₂    _(r), CF₃  (IV)-   (iii) a compound having a chemical structure represented by the    following formula (V):    -Z    OCFX    _(q)    OCF₂CFY    _(q), O-T  (V)    -   wherein structural units (OCFX) and (OCF₂ CFY) in formula (V)        are statistically distributed along a chain. T is a        perfluoroalkyl group containing 1 to 3 carbon atoms, and it        arbitrarily has one H or Cl. X and Y is F or CF₃, and Z is —CFX—        or —CF₂ CFY—. Further, each of q and q′ is an integer of 0 to        10, and the values are identical with or different from each        other, wherein the number average molecular weight of the        monomer of a fluoride is 200 to 2,000.

In (1), (2), (3) and (4) above, the preferred ranges of the value of themolecular formulas, copolymerization ratio and number average molecularweight are defined as above described. If these values are less than thelower limit of the above range, thickening ability sufficient to convertthe grease composition into a grease state is not imparted to thetetrafluoroethylene copolymer. In contrast, if these values are morethan the upper limit of the above range, the grease composition gets sohardened that it becomes difficult for the grease composition to exertsufficient lubricating ability.

Specific examples of such a fluoro resin include polytetrafluoroethylene(PTFE), perfluoroalkoxy alkane (PFA), a perfluoroethylene propenecopolymer (PFEP), an ethylene-tetrafluoroethylene copolymer (FTFE),polyvinylidene fluoride (PVDF), a polychlorotrifluoroethylene-perfluorodioxol copolymer (ECTFE), a polytetrafluoroethylene-perfluoro dioxolcopolymer (TFE/PDD), polyvinyl fluoride (PVE) and others. Of these, PTFEis the most preferable because of its excellent mass productivity.

Metallic Soap and Complex Metallic Soap:

An example of a metallic soap used as a thickener (second thickenercomponent) together with a fluoro resin in the present inventionincludes an aliphatic monobasic metal salt which is synthesized from a1-, 2- or 13-group metal according to the periodic table, and higherfatty acid containing 10 or more carbon atoms or higher hydroxyfattyacid containing one or more hydroxyl group(s) and 10 or more carbonatoms.

Examples of the metal include lithium, sodium, calcium, barium, aluminumand others. Examples of the higher fatty acid include lauric acid,myristic acid, palmitic acid, margaric acid, stearic acid, arachidicacid, behenic acid, lignoceric acid, tallow fatty acid and others.Examples of the higher hydroxyfatty acid include 9-hydroxystearic acid,10-hydroxystearic acid, 12-hydroxystearic acid, 9,10-dihydroxystearicacid and others. Of these aliphatic monobasic acids, 12-hydroxystearicacid is the most preferable in terms of the stability of the thickener.

An example of a complex metallic soap used as a thickener (secondthickener component) together with a fluoro resin in the presentinvention includes a complex metallic soap which is synthesized bysaponifying a 1-, 2- or 13-group metallic hydroxide according to theperiodic table and the mixture of fatty acid and dibasic acid. Examplesof the metal include lithium, sodium, calcium, barium, aluminum andothers. A grease composition comprising the above described complexmetallic soap has a higher dropping point than that of a greasecomposition comprising an ordinary metallic soap, and it is excellent inheat resistance.

This metallic soap and complex metallic soap may be dispersed in a baseoil after they are synthesized separately, or may be dispersed in a baseoil by synthesizing them in the base oil. However, a thickener is betterdispersed in a base oil by the latter method, and so the latter methodis advantageous in the industrial production of a grease composition.

N-Substituted Terephthalamic Acid Metal Salt:

An N-substituted terephthalamic acid metal salt used as a thickener(second thickener component) together with a fluoro resin in the presentinvention is represented by the following general formula (VI):

In the general formula (VI), a substituent R binding to a nitrogen atomis a straight chain, branched chain or cyclic, saturated or unsaturated,monovalent hydrocarbon group, M is a metal, and n denotes a numberequivalent to the valence of the metal.

When the substituent R is a straight or branched chain hydrocarbongroup, the hydrocarbon group contains 10 to 32, preferably 12 to 22carbon atoms, and when the substituent R is a cyclic hydrocarbon group,the hydrocarbon group contains 6 to 28, preferably 7 to 22 carbon atoms.If the number of carbon atoms of the hydrocarbon group is smaller thanthe above described minimum value, the thickener is hardly dispersed ina base oil and further the thickener is likely to separate from the baseoil. To the contrary, if the number of carbon atoms of the hydrocarbongroup is greater than the above maximum value, then the production ofthe thickener is industrially unrealistic.

Examples of the substituent R include a decyl group, a tetradecyl group,a hexadecyl group, an octadecyl group, a cyclohexyl group, a benzylgroup, a phenyl group, a tolyl group, a butylphenyl group and others.Examples of the metal M include 1-, 2-, 12- and 13-group metalsaccording to the periodic table, and examples of such a metal includelithium, potassium, sodium, magnesium, calcium, barium, zinc, aluminumand others. Of these, sodium, barium, lithium and potassium areparticularly preferable, and sodium is the most preferable because ofits excellent mass productivity.

Such an N-substituted terephthalamic acid metal salt may be synthesizedseparately and then dispersed in a base oil, or may be dispersed in thebase oil by synthesis in the base oil. However, since the thickener isbetter dispersed in a base oil by the latter method, when the thickeneris industrially produced, the latter method is advantageous.

Organic Bentonite:

Organic bentonite used as a thickener (second thickener component)together with a fluoro resin in the present invention is one type ofcolloidal clay which is naturally produced, and it is obtained bytreating bentonite that is ferro silicate (laminar silicate) such asmontmorillonite with a cationic surfactant. When bentonite is treatedwith a cationic surfactant, organic molecules are adsorbed between thecrystalline layers of the bentonite so as to obtain lipophilic organicbentonite which swells well in an organic liquid in the presence of apolar dispersing agent.

Bentonite, an important element constituting organic bentonite, iscomplicated silicate containing a large amount of water ofcrystallization and has a structure containing the layers of ionalignments laminated in parallel. That is, two silicate layers aredisposed in parallel, and a layer of alkaline metal, alkaline earthmetal or water molecules is interposed between the silicate layers. Morespecifically, in the above layer has a three-layer structure, twotetrahedral layers of Si are disposed in parallel, with the tetrahedronsopposing to each other on the vertexes, and an octahedral layer of Al isinterposed between the tetrahederal layers.

In such bentonite, since the binding strength between the metal ionlocating in the interlamillar portion and the silicate is relativelyweak, an ion exchange reaction occurs, for example, between aquarternary ammonium salt and the metal ion, by treatment with acationic surfactant, and as a result, what is called organic bentoniteis obtained. By this reaction, hydrophilic bentonite is changed tolipophilic one.

A production method of organic bentonite and the like are disclosed indetail, for example, in Japanese Patent Laid-Open Nos. 62-83108 and53-72792.

Organic bentonite may be synthesized separately and then dispersed in abase oil, or may be dispersed in the base oil by synthesis in the baseoil. However, since the thickener is better dispersed in a base oil bythe latter method, when the thickener is industrially produced, thelatter method is advantageous.

Calcium Sulfonate Complex:

A calcium sulfonate complex used as a thickener (second thickenercomponent) together with a fluoro resin in the present inventioncomprises calcium sulfonate as an essential component, and alsocomprises at least one type of calcium salt (calcium soap) selected froma group consisting of (a) calcium carbonate, (b) a higher fatty acidcalcium salt such as calcium dibehenate, calcium distearate and calciumdihydroxystearate, (c) a lower fatty acid calcium salt such as calciumacetate, and (d) calcium borate.

It is particularly preferable to use a calcium sulfonate complex, whichcomprises calcium sulfonate and calcium carbonate as essentialcomponents and also comprises two or more selected from a groupconsisting of calcium dibehenate, calcium distearate, calciumdihydroxystearate, calcium acetate and calcium borate.

In terms of thickening effect, the above described calcium sulfonatepreferably has a base number of 50 to 500 mgKOH/g, and more preferablyit is overbased calcium sulfonate with a base number of 300 to 500mgKOH/g.

The calcium sulfonate complex may be dispersed in a base oil after it issynthesized separately, or the calcium sulfonate complex may also bedispersed in a base oil by synthesis in the base oil. However, since thethickener is better dispersed in a base oil by the latter method, whenthe thickener is industrially produced, the latter method isadvantageous.

Carbon Black:

Carbon black used as a thickener (second thickener component) togetherwith a fluoro resin in the present invention acts as an electricconductivity imparting additive as well as a thickener in the greasecomposition.

The type of carbon black to be used is not particularly limited, butconsidering ability to impart thickening capacity and electricconductivity to the grease composition, carbon black having large oilabsorption capacity (DBP oil absorption being 100 ml/100 g or more) ispreferable. Moreover, it is preferable to use carbon black havinglipophilic property and a large specific surface area (the primaryparticle size being less than 100 nm and the specific surface area being50 m²/g or larger.)

If the DBP oil absorption, primary particle size and specific surfacearea of carbon black are out of the above range, there is a risk thatthe thickening capacity and electric conductivity of the greasecomposition might become insufficient. The above specific surface areais determined by e.g. nitrogen adsorption method.

Specific examples of the carbon black include acetylene black, Ketjenblack, channel black and others. Of these, acetylene black isparticularly preferable, since it has a developed carbon structure bythermal decomposition.

This carbon structure consists of primary particles (the averageparticle size being 0.026 to 0.042 μm by electron microscopy), in whichcrystallites obtained by the lamination of net planes of carbons areaggregated. A large number of the primary particles are connected toconstruct a chain or resinous structure. Of these acetylene black, onehaving a significantly small amount of hydrogen that is considered tofix the motion of π electrons is preferable. Of commercially availableacetylene black, easy-to-handle granular acetylene black as well aspowder acetylene black may be used. Not only acetylene black but alsoother carbon black such as gas black can be used, as long as they havethe developed carbon structure as described above.

Base Oil:

The type of a base oil used in the grease composition of the presentinvention is not particularly limited, but the base oil preferablycomprises at least one of either a mineral oil or synthetic oil and aperfluoropolyether oil. However, other types of oils may be used incombination to such an extent that it does not impair the purpose of thepresent invention.

The type of the mineral oil is not particularly limited, but a paraffinmineral oil, a naphthene mineral oil, a mixed oil thereof, and others,are preferably used. The type of the synthetic oil is also notparticularly limited, a synthetic hydrocarbon oil, an ether oil, anester oil, a fluoro oil and others are preferably used.

Specific examples of the synthetic hydrocarbon oil include a polyα-olefin oil, a cooligomer synthetic oil of α-olefin and ethylene, andothers.

An example of the ether oil includes a phenyl ether oil substituted byan alkyl group(s) containing 12 to 20 carbon atoms (e.g. a diphenylether oil, a triphenyl ether oil, a tetraphenyl ether oil, etc.). Thenumber of alkyl groups substituted is not particularly limited, but oneor two are preferable. Taking into consideration the low vaporizabilityof the base oil, an alkyl diphenyl ether oil is preferable.

Examples of the fluoro oil include a perfluoroether oil and a derivativethereof, a fluorosilicone oil, a chlorotrifluoroethylene oil, afluorophosphazene oil and others.

Moreover, examples of the ester oil include a diester oil, a polyolester oil (e.g. a neopentyl-type polyol ester oil, etc.), a complexester oil thereof, an aromatic ester oil, a carbonate oil and others.

The diester oil is obtained by a reaction between dibasic acid andalcohol, and examples of the diester oil include dioctyl adipate,diisobutyl adipate, dibutyl adipate, dibutyl sebacate, dioctyl sebacate,methylacetyl ricinolate and others.

Moreover, the polyol ester oil is obtained by a reaction between polyoland one or two or more types of monobasic acid. A complex ester that isoligo ester obtained by a reaction between a mixed fatty acid ofmonobasic acid and dibasic acid and polyol may also be used.

Examples of the polyol include trimethylolpropane, pentaerythritol,dipentaerythritol, neopentyl glycol, 2-methyl-2-propylpropane-1,3-diol,and others.

A preferred example of the monobasic acid includes fatty acid containing4 to 18 carbon atoms, and specific examples include valeric acid,caproic acid, caprylic acid, enanthic acid, pelargonic acid, capricacid, undecanoic acid, lauric acid, myristic acid, palmitic acid, tallowfatty acid, stearic acid, caproleic acid, undecylenic acid, lindericacid, tsuzuic acid, physeternic acid, myristoleic acid, palmitoleicacid, petroselinic acid, oleic acid, elaidic acid, asclepinic acid,vaccenic acid, sorbic acid, linolic acid, linolenic acid, sabinic acid,ricinoleic acid and others.

Examples of the aromatic ester oil include trimellitic acid ester suchas trioctyl trimellitate or tridecyl trimellitate, and pyromellitic acidester such as tetraoctyl pyromellitate.

The type of the perfluoropolyether oil used in the grease composition isnot particularly limited, but the perfluoropolyether oil is preferablycomprised of at least one type selected from the following fluorooxyalkylene structural units. In the following formulas, X₃ representsCF₃(CF₂)_(n)—, and n represents an integer of 0 to 4.

-   CF₂CF₂O    ,    CF₂O-   CF₂CF(CF₃)O    ,    CF(CF₃)O-   CF₂CF₂CF₂O    ,    CF₂CF(OX₃)O-   CF(OX₃)O

When the perfluoropolyether oil is comprised of two or more types of theabove fluorooxy alkylene structural units, each structural unit isstatistically distributed along a chain. The terminal group thereof is afluoroalkyl group arbitrarily having an H and/or a Cl such as CF₃—,C₂F₅—, C₃F₇—, CF₂Cl(CF₃)CF—, CF₃CFClCF₂—, CF₂ClCF₂—, CF₂Cl—, CHF₂— orCF₃CHF—.

Each of the above described various base oils may be used singly, or maybe used appropriately in combination of two or more types. Taking intoconsideration the lubricating ability and life of the rolling apparatusunder high-temperature and high-speed conditions into which the greasecomposition is enclosed, it is preferable that a synthetic oil iscontained in the base oil, and it is more preferable that at least onetype selected from an ester oil, an ether oil and a fluoro oil iscontained in the base oil. Of the ester oils, a polyol ester oil and anaromatic ester oil are further preferable, of the ether oils, analkyldiphenyl ether oil is further preferable, and of the fluoro oils, aperfluoroether oil, a derivative thereof and a fluorophosphazene oil arefurther preferable.

Additive:

Various additives may be added, as desired, to the grease composition ofthe present invention so as to improve various performances of thegrease composition. For example, additives such as an antioxidant, arust preventive, an extreme-pressure additive, an oiliness improver anda metal deactivator, which are generally used for grease compositions,can be used singly or in combination of two or more.

Examples of the antioxidant include amine antioxidants, phenolantioxidants, sulfur antioxidants, zinc dithiophosphate and others.

Specific examples of an amine antioxidant includephenyl-1-naphthylamine, phenyl-2-naphthylamine, diphenylamine,phenylenediamine, oleyl amide amine, phenothiazine and others.

Specific examples of a phenol antioxidant include hindered phenols orthe like such as p-t-butylphenyl salicylate, 2,6-di-t-butylphenol,2,6-di-t-butyl-p-phenylphenol,2,2′-methylenebis(4-methyl-6-t-octylphenol),4,4′-butylidenebis-6-t-butyl-m-cresol, tetrakis{methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate}methane,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,n-octadecyl-β-(4′-hydroxy-3′,5′-di-t-butylphenyl)propionate,2-n-octyl-thio-4,6-di(4′-hydroxy-3′,5′-di-t-butyl)phenoxy-1,3,5-triazine,4,4′-thiobis(6-t-butyl-m-cresol),2-(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole andothers.

Examples of a rust preventive include petroleum sulfonate, an organicsulfonic acid metal salt (herein, metal is an alkali metal,alkaline-earth metal or the like), esters and others.

Specific examples of an organic sulfonic acid metal salt include themetal salt of dinonylnaphthalene sulfonic acid or heavy alkylbenzenesulfonic acid (calcium sulfonate, barium sulfonate, sodium sulfonate,etc.), and others.

Specific examples of esters include sorbitan esters such as sorbitanmonolaurate, sorbitan tristearate, sorbitan monooleate and sorbitantrioleate, which are the partial esters of polybasic carboxylic acid andpolyol; alkyl esters such as polyoxyethylene laurate, polyoxyethyleneoleate and polyoxyethylene stearate; and others.

Moreover, alkyl succinic acid derivatives and alkenyl succinic acidderivatives such as alkyl succinic acid ester and alkenyl succinic acidester can also preferably be used as rust preventives.

The grease composition of the present invention has a rust protectionproperty by itself, but the rust protection property is further improvedby adding the above rust preventives.

Furthermore, examples of an extreme-pressure additive include phosphorusextreme-pressure additives, zinc dithiophosphate, organic molybdenum andothers.

Still further, examples of an oiliness improver include fatty acid suchas oleic acid or stearic acid; alcohol such as lauryl alcohol or oleylalcohol; amine such as stearylamine or cetylamine; phosphoric ester suchas tricresyl phosphate; animal and vegetable oils; and others.

Still further, an example of a metal deactivator includes benzotriazoleor the like.

The additive amount of these additives is not particularly limitedunless it impairs the purpose of the present invention, but it ispreferably 20% or less by mass based on the total mass of the greasecomposition. If the additive amount exceeds 20% by mass, the additiveeffects are not improved, and there is also a risk that the lubricatingability might lower since the amount of a base oil is relativelyreduced.

The production method of the grease composition of the present inventionis not particularly limited. For example, a fluoro grease comprising aperfluoropolyether oil as a base oil and a fluoro resin as a thickener;and a grease composition comprising at least one of either a mineral oilor synthetic oil as a base oil and a second thickener component such asa metallic soap or carbon black as a thickener, are produced separately,and these are then mixed. Otherwise, the grease composition of thepresent invention can also be produced by adding the fluoro resin andthe second thickener component as thickeners into the base oil obtainedby mixing the perfluoropolyether oil and at least one of either themineral oil or synthetic oil.

The former method is a method of mixing the previously produced greasecomposition, and therefore the fluoro oil can be used as a base oil.Moreover, in the latter method, the fluoro oil can be used, if theamount is within 5 volume % based on the total volume of the base oil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial longitudinal sectional view showing theconfiguration of a deep groove ball bearing, which is one embodiment ofthe rolling apparatus of the present invention;

FIG. 2 is a schematic diagram showing the configuration of an apparatusfor evaluating the amount of dusts generated from a bearing;

FIG. 3 is a schematic diagram showing the configuration of a torquemeasuring apparatus;

FIG. 4 is an oblique perspective view of a continuous rotating apparatusfor evaluating the durability of a bearing;

FIG. 5 is a partial front view of the continuous rotating apparatus ofFIG. 4;

FIG. 6 is a graph showing the correlation between the ratio of PTFE in athickener, and the amount of dusts generated and durability of a greasecomposition, in the case of using a grease composition comprising ametallic soap as the second thickener component;

FIG. 7 is a graph showing the correlation between the content of athickener based on the total mass of a grease composition, and theamount of dusts generated and durability of the grease composition, inthe case of using a grease composition comprising a metallic soap as thesecond thickener component;

FIG. 8 is a longitudinal sectional view showing the configuration of aball bearing, which is another embodiment of the rolling apparatus ofthe present invention;

FIG. 9 is a cross-sectional view showing the configuration of a bearinglife test machine for evaluating the seizuring ability of a greasecomposition;

FIG. 10 is a graph showing the correlation between the ratio of a fluororesin in a thickener, and the seizuring life of a ball bearing and therust protection of a grease composition, in the case of using a greasecomposition comprising an N-substituted terephthalamic acid metal saltas the second thickener component;

FIG. 11 is a graph showing the correlation between the ratio of a fluororesin in a thickener, and the seizuring life of a ball bearing and theamount of grease leaked, in the case of using a grease compositioncomprising an N-substituted terephthalamic acid metal salt as the secondthickener component;

FIG. 12 is a graph showing the correlation between the ratio of organicbentonite in a thickener, and the rust protection and lubricating lifeof a grease composition, in the case of using a grease compositioncomprising organic bentonite as the second thickener component;

FIG. 13 is a graph showing the correlation between the content of athickener based on the total mass of the grease composition and thelubricating life, in the case of a grease composition comprising organicbentonite as the second thickener component;

FIG. 14 is a longitudinal sectional view showing the configuration of aball bearing, which is another embodiment of the rolling apparatus ofthe present invention;

FIG. 15 is a partial longitudinal sectional view showing theconfiguration of a ball bearing, which is another embodiment of therolling apparatus of the present invention;

FIG. 16 is a schematic block diagram of an apparatus for measuring theelectric resistance value of a bearing;

FIG. 17 is a graph showing the correlation between the ratio of a fluororesin in a thickener, and the seizuring life of a ball bearing and therust protection of a grease composition, in the case of using a greasecomposition comprising carbon black as the second thickener component;and

FIG. 18 is a graph showing the correlation between the ratio of a fluororesin in a thickener, and the seizuring life and electric resistancevalue of a ball bearing, in the case of using a grease compositioncomprising carbon black as the second thickener component.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the grease composition and the rolling apparatus ofthe present invention will be explained in detail, while referring tofigures.

(A) Grease Composition Comprising Fluoro Resin and Metallic Soap asThickener

Tables 1 to 3 show the compositions of the grease compositions ofExamples and Comparative examples. NLGI worked penetration of eachgrease composition is also shown in the tables. The worked penetrationis determined according to JIS K2220. TABLE 1 Example Example ExampleExample Example Example A1 A2 A3 A4 A5 A6 Type of Li soap²⁾ 60 30 80 3030 — thickener¹⁾ Ca soap³⁾ — — — 30 — 30 Na soap⁴⁾ — — — — 30 30 PTFE⁵⁾40 70 20 40 40 40 Content of thickener¹⁾ 23 29 19 24 24 25 Type of basePOE oil⁶⁾ 60 30 80 60 60 60 oils¹⁾ PFPE oil⁷⁾ 40 70 20 40 40 40 Contentof base oil¹⁾ 77 71 81 76 76 75 Worked penetration 221 240 210 220 216222 Amount of dusts 25° C. 750 400 900 650 550 500 generated in theearly 70° C. 3250 2100 4400 3550 3250 2700 stage of rotation⁸⁾ Acousticperformance in the ∘ ∘ ∘ ∘ ∘ ∘ early stage of rotation Torque value inthe early ∘ ∘ ∘ ∘ ∘ ∘ stage of rotation Durability(hr) >3000 >3000 >3000 >3000 >3000 >3000 Amount of dusts generated 42003300 5250 3950 3700 3450 after durability test⁸⁾¹⁾Unit of value is % by mass²⁾Lithium 12-hydroxystearate³⁾Calcium 12-hydroxystearate⁴⁾Sodium 12-hydroxystearate⁵⁾Polytetrafluoroethylene⁶⁾Polyol ester oil⁷⁾Perfluoropolyether oil⁸⁾Unit is particles/283 cm³

TABLE 2 Example Example Example Example Example Example A7 A8 A9 A10 AllA12 Type of Li soap²⁾ 60 30 80 30 30 — thickener¹⁾ Ca soap³⁾ — — — 30 —30 Na soap⁴⁾ — — — — 30 30 PTFE⁵⁾ 40 70 20 40 40 40 Content ofthickener¹⁾ 23 29 19 24 24 25 Type of base ADPE oil⁶⁾ 60 30 80 60 60 60oils¹⁾ PFPE oil⁷⁾ 40 70 20 40 40 40 Content of base oil¹⁾ 77 71 81 76 7675 Worked penetration 219 235 203 215 207 214 Amount of dusts 25° C. 650450 800 550 500 450 generated in the early 70° C. 3150 2200 4150 33503200 2400 stage of rotation⁸⁾ Acoustic performance in the ∘ ∘ ∘ ∘ ∘ ∘early stage of rotation Torque value in the early stage ∘ ∘ ∘ ∘ ∘ ∘ ofrotation Durability (hr) >3000 >3000 >3000 >3000 >3000 >3000 Amount ofdusts generated after 4000 3350 5150 3750 3550 3300 durability test⁸⁾¹⁾Unit of value is % by mass²⁾Lithium 12-hydroxystearate³⁾Calcium 12-hydroxystearate⁴⁾Sodium 12-hydroxystearate⁵⁾Polytetrafluoroethylene⁶⁾Alkyl diphenyl ether oil⁷⁾Perfluoropolyether oil⁸⁾Unit is particles/283 cm³

TABLE 3 Comparative Comparative Comparative Example Example Exampleexample example example A13 A14 A15 A1 A2 A3 Type of Li soap²⁾ 20 60 60100 — — thickener¹⁾ Ca soap³⁾ — — — — 100 — Na soap⁴⁾ — — — — — — PTFE⁵⁾80 40 40 — — 100 Content of thickener¹⁾ 30 41 9 15 18 35 Type of baseADPE oil⁶⁾ 20 60 60 100 100 — oils¹⁾ PFPE oil⁷⁾ 80 40 40 — — 100 Contentof base oil¹⁾ 70 59 91 85 82 65 Worked penetration 220 170 300 224 217245 Amount of dusts 25° C. 300 200 1800 2400 3000 150 generated in theearly 70° C. 1800 1500 6750 9000 12000 1200 stage of rotation⁸⁾ Acousticperformance in the ∘ ∘ ∘ ∘ ∘ x early stage of rotation Torque value inthe early stage ∘ x ∘ ∘ ∘ x of rotation Durability (hr)2500 >3000 >3000 >3000 Amount of dusts generated 35000 23000 33000 afterdurability test⁸⁾¹⁾Unit of value is % by mass²⁾Lithium 12-hydroxystearate³⁾Calcium 12-hydroxystearate⁴⁾Sodium 12-hydroxystearate⁵⁾Polytetrafluoroethylene⁶⁾Alkyl diphenyl ether oil⁷⁾Perfluoropolyether oil⁸⁾Unit is particles/283 cm³

The compositions of the grease compositions of Examples A1 to A15 andComparative examples A1 to A3 are as shown in Tables 1 to 3, and eachcomposition comprises a thickener consisting of a metallic soap and afluoro resin (PTFE), and a base oil consisting of a synthetic oil and aperfluoropolyether oil (PFPE oil) (except Comparative examples A1 toA3). The metallic soap is the lithium salt, calcium salt or sodium saltof 12-hydroxystearic acid, but a complex metallic soap can also be usedinstead of the metallic soap. The synthetic oil is a polyolester oil(POE oil) or alkyldiphenylether oil (ADPE oil), and regarding thekinematic viscosity of each oil at 40° C., the POE oil has 70 mm²/s, theADPE oil has 100 mm²/s, and the PFPE oil has 190 mm²/s.

Although not described in each table, each grease composition comprises,as additives, 1.0% by mass of an amine antioxidant, 0.5% by mass of acalcium sulfonate rust preventive and 0.05% by mass of a benzotriazolemetal deactivator based on the total mass of the grease composition.

It should be noted that the content (% by mass) of the base oil and thethickener described in each of Tables 1 to 3 is a value based on thatthe total mass of the base oil and the thickener is defined as 100, andthat the above additives are not considered. Moreover, values describedin the columns of the type of thickener and the type of base oil showthe mass ratio of each component constituting the thickener and the massratio of each component constituting the base oil, respectively, in acase where each of the total mass (% by mass) of the thickener and thetotal mass of the base oil is defined as 100.

Rolling bearings filled with each of the above 18 types of greasecompositions were prepared, and acoustic performance, torqueperformance, durability, and the amount of dusts generated therefromwere evaluated.

The used rolling bearing was a single-row deep groove ball bearing 10(inside diameter: 5 mm, outside diameter: 13 mm, width: 4 mm) completelydefatted by organic solvent, and this rolling bearing was comprised of:an inner ring 1; an outer ring 2; a plurality of balls 3, which weredisposed between the inner ring 1 and the outer ring 2 to flexibly rolltherebetween; a cage 4 for retaining the plurality of balls 3 betweenthe inner ring 1 and the outer ring 2; and noncontact rubber seals 5, 5installed in the seal groove 2 a, 2 a of the outer ring 2 (refer to thepartial cross-sectional view of FIG. 1). A space portion, which wassurrounded by the inner ring 1, the outer ring 2 and the rubber seals5,5 of the ball bearing 10, was filled with 19 mg of the above greasecomposition G, and the rubber seals 5, 5 hermetically sealed the greasecomposition in the ball bearing 10.

Next, methods of evaluating each of the above various performances willbe explained below.

Method for Evaluating the Amount of Dusts Generated from GreaseComposition:

As shown in FIG. 2, the inner ring 1 of the ball bearing 10 was mountedon a rotation shaft 21, and the outer ring 2 was mounted on a container22. The container 22 comprised an air introduction port 22 a and an airdischarge port 22 b, and clean air was flown into the container 22through the air introduction port 22 a, and then the air was flown outof the container 22 through the air discharge port 22 b.

When the rotation shaft 21 was rotated by a motor which is not shown inthe figure and the ball bearing 10 was thereby rotated, dusts weregenerated from the grease composition G contained in the ball bearing10, and the particles of the grease composition were dispersed in thecontainer 22. These particles were flown out of the container 22 by theair which was flown in through the air introduction port 22 a, and thenthe particles were transported to a particle counter which is not shownin the figure. Thereafter, the number of particles having a particlesize of 0.3 μm or greater which were contained in 0.01 cubic feet (283cm³) of the air, was counted by this particle counter.

The ball bearing 10 was mounted on the container 22 under the conditionwhere a preload of 14.7 N was loaded. Moreover, the rotational speed ofthe ball bearing 10 was set at 3,600 min⁻¹. Under these conditions, theamount of dusts generated was counted both at 25° C. and at 70° C. for20 minutes.

Thus, the amount of dusts generated in the early stage of rotation of aball bearing 10, which was counted as above, is also shown in Tables 1to 3.

Method for Evaluating Acoustic Performance:

The acoustic performance of the ball bearing 10 in the early stage ofrotation (the rotational speed was 1,800 min⁻¹) was evaluated using anAnderon Meter. The results are also shown in Tables 1 to 3. In eachtable, when the Anderon value is 2 or less, it is evaluated assatisfactory and shown with the mark ◯, and when the Anderon value ismore than 2, it is evaluated as unsatisfactory and shown with the markx.

Method for Evaluating Torque Performance:

Using a torque measuring device shown in FIG. 3, the torque value of theball bearing 10 was determined in the early stage of rotation. The innerring of the ball bearing 10 was fixed to an air spindle 41 via an arbor42, and the outer ring was fixed to an aluminum cap 44 which wasequipped with an air bearing 43. The air spindle 41 was rotated at arotational speed of 3,600 min⁻¹ at a room temperature so as to rotatethe inner ring of the ball bearing 10. At the time when the torque valuewas almost stabilized (about 10 minutes later), the torque value wasdetermined by a strain gauge 45 which was connected to the aluminum cap44. The obtained value was recorded by a recorder 48 via a strain amp 46and a low-pass filter 47.

The obtained results are also shown in Tables 1 to 3. In each table,when the torque value is 29.4 N·cm or less, it is evaluated assatisfactory and shown with the mark 0, and when the torque value ismore than 29.4 N·cm, it is evaluated as unsatisfactory and shown withthe mark x.

Method for Evaluating Durability:

The ball bearing 10 (not shown) was mounted in the housing 51 of acontinuous rotating apparatus having a configuration shown in theoblique perspective view of FIG. 4 and the partial front view of FIG. 5,and rotated by a motor 54 via a rubber belt 52 and a pulley 53. Therotational speed was 3,600 min⁻¹ and the test temperature was 70° C. TheAnderon value of the ball bearing 10 was determined using an AnderonMeter every 500 hours of rotation, and the life was defined as a timewhen the Anderon value exceeded 2. However, where the Anderon value didnot exceed 2 even after 3,000 hours, the test was terminated.

As well as the above described evaluation of acoustic durability, theevaluation of the amount of dusts generated from a grease compositionwas also carried out. That is, the amount of dusts generated from agrease composition at the time of the completion of the durability test(after rotation at a high temperature for a long time) was determined bythe same method as described above.

The evaluation results of the durability and the amount of dustsgenerated from a grease composition after rotation at a high temperaturefor a long time are also shown in Tables 1 to 3. Where “>3,000” which isdescribed in the column of durability means that the durability test wasterminated after 3,000 hours of rotation.

Now, the results of each test will be considered. As apparent fromTables 1 to 3, the grease compositions in Examples A1 to A12 generated asmall amount of dusts in the early stage of rotation both at an ordinarytemperature and at a high temperature, and even when the greasecompositions were subjected to rotation at a high temperature for a longtime, the amount of dusts generated was not significantly increased.Further, their acoustic performance and torque value were excellent inthe early stage of rotation, and also their durability was extremelyexcellent.

In contrast, since Comparative examples A1 and A2 did not comprise PTFEas a thickener, a large amount of dusts was generated in the initialrotation stage. Moreover, the amount of dusts generated furtherincreased by rotation at a high temperature for a long time.

Comparative example A3 generated a small amount of dusts, but since itdid not comprise a metallic soap as a thickener, the acousticperformance and torque value in the initial rotation stage wereunsatisfactory, and durability was also insufficient.

Example A13 was excellent in the amount of dusts generated, acousticperformance and torque value in the initial rotation stage. However,since the amount of the mineral oil and the synthetic oil in the baseoil was smaller than the case of the perfluoropolyether oil, it wassomewhat poor in durability.

Example A14 had a small amount of dusts generated and good acousticperformance in the initial rotation stage, but since the workedpenetration was small, the torque value in the initial rotation stagewas unsatisfactory.

Example A15 had good acoustic performance, torque value in the initialrotation stage and durability, but since the worked penetration waslarge, it generated a large amount of dusts in the initial rotationstage both at an ordinary temperature and at a high temperature, andfurther, the amount of dusts significantly increased when rotated at ahigh temperature for a long time in comparison with the greasecompositions in Examples A1 to A12.

Next, the ratio between a metallic soap and PTFE in a thickener wasstudied. That is to say, grease compositions were prepared by variouslychanging the ratio between the metallic soap and PTFE in the greasecomposition of Example A1, and the amount of dusts generated at 70° C.in the initial rotation stage and durability were evaluated by the samemethod as described above. The results are shown in the graph of FIG. 6.

The graph of FIG. 6 shows that when the ratio of PTFE in a thickener was10 to 80% by mass, the grease composition was excellent in both theamount of dusts generated at 70° C. in the initial rotation stage anddurability, and when the ratio was 20 to 70% by mass, the above bothperformances were more excellent.

Next, the content of a thickener based on the total mass of a greasecomposition was studied. That is to say, grease compositions wereprepared by variously changing the content of the thickener in thegrease composition of Example A1, and the amount of dusts generated at70° C. in the initial rotation stage and durability were evaluated bythe same method as described above. The results are shown in the graphof FIG. 7.

The graph of FIG. 7 shows that when the content of the thickener was 10to 33% by mass, the grease composition was excellent in both the amountof dusts generated at 70° C. in the initial rotation stage anddurability, and when the content was 15 to 30% by mass, the above bothperformances were more excellent.

(B) Grease Composition Comprising Fluoro Resin and N-SubstitutedTerephthalamic Acid Metal Salt as Thickener

FIG. 8 is a longitudinal sectional view showing the configuration of aball bearing 101, which is one embodiment of the rolling apparatus ofthe present invention. This ball bearing 101 is comprised of an innerring 110; an outer ring 111; a plurality of balls 113, which aredisposed between the inner ring 110 and the outer ring 111 so as toflexibly roll therebetween; a cage 112 for retaining the plurality ofballs 113; and contact seals 114,114 installed in the outer ring 111. Aspace portion, which is surrounded by the inner ring 110, the outer ring111 and the seals 114,114, is filled with a grease composition G, andthe seal 114 hermetically sealed the grease composition in the ballbearing 101. This grease composition G lubricates the contact surfacebetween the raceway surfaces of both rings 110 and 111, and the balls113.

The grease composition G comprises 20% by mass of a thickener and 80% bymass of a base oil. The thickener comprises 50% by mass of anN-substituted terephthalamic acid metal salt and 50% by mass of PTFE,and the base oil comprises 50% by mass of a polyol ester oil and 50% bymass of a perfluoropolyether oil (PFPE oil). Since the greasecomposition G comprises the PTFE and the PFPE oil, it has excellent heatresistance.

Since a rolling apparatus such as a ball bearing filled with this greasecomposition has excellent lubricating ability and is long-lived underhigh temperature conditions, it can preferably be used as a rolling orsliding portion of machines used under high-temperature and high-speedconditions including car electrical components such as alternators orelectromagnetic clutches; auxiliary equipment for car engine such asidler pulleys; and business machines such as copying machines orprinters.

Next, with regard to 18 types of grease compositions (Examples B1 toB12, and Comparative Examples B1 to B6) which have almost the samecomposition as the above described grease composition G, a workedpenetration determination, a rust protection test, a copper corrosiontest, a seizure test and a grease leakage test were carried out.

The compositions of the grease compositions of Examples B1 to B12 andComparative examples B1 to B6 are as shown in Tables 4 to 6, and eachgrease composition comprises a thickener consisting of N-octadecylterephthalamic acid metal salt (sodium salt or barium salt) and a fluororesin (PTFE or a copolymer), and a base oil consisting of a syntheticoil and a PFPE oil (excluding Comparative examples B1 and B2). Eachgrease composition further comprises, as additives, 1.0% by mass of anamine antioxidant, 0.5% by mass of a calcium sulfonate rust preventiveand 0.05% by mass of a benzotriazole metal deactivator based on thetotal mass of the grease composition. TABLE 4 Example Example ExampleExample Example Example B1 B2 B3 B4 B5 B6 Type of Terephthalamic acid 50— 20 50 60 — thickener¹⁾ Na²⁾ Terephthalamic acid — 50 — — — 50 Ba³⁾PTFE 50 50 80 — — — Copolymer⁴⁾ — — — 50 40 50 Content of thickener¹⁾ 2525 30 25 24 25 Type of base POE oil⁵⁾ 50 50 20 50 60 50 oils¹⁾ ADPEoil⁵⁾ — — — — — — PFPE oil 50 50 80 50 40 50 Content of base oil¹⁾ 75 7570 75 76 75 Worked penetration 268 275 270 273 272 279 Copper corrosiontest 1 1 1 1 1 1 Rust protection test #6 #6 #5 #6 #6 #6 Seizure test(for life)⁷⁾ 1274 1199 1612 1231 1098 1167 Grease leakage test¹⁾ 3.5 3.62.8 3.4 3.5 3.5¹⁾Unit is % by mass²⁾N-octadecylterephthalamic acid sodium salt³⁾N-octadecylterephthalamic acid barium salt⁴⁾Copolymer of vinylidene fluoride and hexafluoroisobutylene (molarratio 1:1)⁵⁾Polyol ester oil⁶⁾Alkyl diphenyl ether oil⁷⁾Unit is hr

TABLE 5 Example Example Example Example Example Example B7 B8 B9 B10 B11B12 Type of Terephthalamic acid 50 — 20 50 60 — thickener¹⁾ Na²⁾Terephthalamic acid — 50 — — — 50 Ba³⁾ PTFE 50 50 80 — — — Copolymer⁴⁾ —— — 50 40 50 Content of thickener¹⁾ 25 25 30 25 24 25 Type of base POEoil⁵⁾ — — — — — — oils¹⁾ ADPE oil⁶⁾ .50 50 20 50 60 50 PFPE oil 50 50 8050 40 50 Content of base oil¹⁾ 75 75 70 75 76 75 Worked penetration 268275 270 273 272 279 Copper corrosion test 1 1 1 1 1 1 Rust protectiontest #6 #6 #5 #6 #6 #6 Seizure test (for life)⁷⁾ 1688 1632 1722 15951534 1521 Grease leakage test¹⁾ 3.5 3.4 2.8 3.4 3.5 3.5¹⁾Unit is % by mass²⁾N-octadecylterephthalamic acid sodium salt³⁾N-octadecylterephthalamic acid barium salt⁴⁾Copolymer of vinylidene fluoride and hexafluoroisobutylene (molarratio 1:1)⁵⁾Polyol ester oil⁶⁾Alkyl diphenyl ether oil⁷⁾Unit is hr

TABLE 6 Comparative Comparative Comparative Comparative ComparativeComparative example example example example example example B1 B2 B3 B4B5 B6 Type of Terephthalamic acid — 100 50 80 70 — thickener¹⁾ Na²⁾Terephthalamic acid — — — — — 50 Ba³⁾ PTFE 100 — 50 — — — Copolymer⁴⁾ —— — 20 30 50 Content of thickener¹⁾ 35 15 3 20 23 42 Type of base POEoil⁵⁾ — — — — — — oils¹⁾ ADPE oil⁵⁾ — 100 50 80 70 50 PFPE oil 100 — 5020 30 50 Content of base oil¹⁾ 65 85 97 80 77 58 Worked penetration 293267 — 271 272 190 Copper corrosion test 4 1 — 1 1 1 Rust protection test#1 #7 — #7 #6 #6 Seizure test (for life)⁷⁾ 1743 375 — 737 891 689 Greaseleakage test¹⁾ 2.3 4.5 — 3.9 3.6 1.1¹⁾Unit is % by mass²⁾N-octadecylterephthalamic acid sodium salt³⁾N-octadecylterephthalamic acid barium salt⁴⁾Copolymer of vinylidene fluoride and hexafluoroisobutylene (molarratio 1:1)⁵⁾Polyol ester oil⁶⁾Alkyl diphenyl ether oil⁷⁾Unit is hr

It should be noted that the contents of the base oil and the thickenerdescribed in Tables 4 to 6 are values based on the total mass of thebase oil and the thickener defined as 100, and therefore the aboveadditives are not considered. Values described in the columns of thetype of thickener and the type of base oil represent mass ratio (% bymass) of each component based on the total mass of the thickener and thetotal mass of the base oil.

Each component of the grease composition will be explained below.

-   -   Copolymer: a copolymer of vinylidene fluoride and        hexafluoroisobutylene (the mole ratio being 1:1)    -   Polyol ester oil: a kinematic viscosity at 40° C. being 70 mm²/s    -   Alkyl diphenyl ether oil: a kinematic viscosity at 40° C. being        100 mm²/s    -   PFPE oil: a kinematic viscosity at 40° C. being 190 mm²/s

Next, each test method and test results will be explained below.

Worked Penetration Determination:

Worked penetration was determined according to JIS K2220.

The results are shown in Tables 4 to 6. The grease compositions inExamples B1 to B12 had good worked penetration. In contrast, since thecontent of the thickener was too large in Comparative example B6, theworked penetration was small. Moreover, since the content of thethickener is too small in Comparative example B3, the grease compositiondid not become a grease state.

Rust Protection Test:

Each of the grease compositions in Examples B1 to B12 and Comparativeexamples B1 to B6 was filled in a deep groove ball bearing with rubberseals having an inside diameter of 17 mm, an outside diameter of 47 mmand a width of 14 mm (having the same configuration as the ball bearingof FIG. 8,) at 50% the volume of the space portion of the ball bearing.

After a running-in (rotation) at a rotational speed of 1,800 min⁻¹ for30 seconds, 0.5 ml of 0.5% by mass of salt water was poured in theinside of the bearing, and another running-in was carried out again at arotational speed of 1,800 min⁻¹ for 30 seconds. Then, this ball bearingwas left at rest for 48 hours in a constant temperature and humiditybath which was controlled at 80° C. and 100% RH, and thereafter, theball bearing was decomposed and the condition of rust generated on theraceway surface was observed by the visual test. The rust condition wasevaluated in the following ranks.

-   #7: Generation of no rust-   #6: Generation of very slight rust stain-   #5: Generation of punctated rust with a diameter of 0.3 mm or    shorter-   #4: Generation of rust with a diameter of 1.0 mm or shorter-   #3: Generation of rust with a diameter of 5.0 mm or shorter-   #2: Generation of rust with a diameter of 10.0 mm or shorter-   #1: Generation of rust on almost the entire surface of the raceway    surface

Herein, #7 to #5 were defined as good rust protection, and #4 to #1 weredefined insufficient rust protection.

The results are shown in Tables 4 to 6. The grease compositions inExamples B1 to B12 showed good rust protection. Accordingly, the greasecompositions in Examples B1 to B12 can preferably be used in a bearing,which is used under strict environment where the bearing readilycontacts with rain water or the like and so readily generates rust. Incontrast, since Comparative example B1 does not contain a mineral oil orsynthetic oil (that is, since it is a common fluoro grease), the rustprotection was insufficient.

Copper Corrosion Test:

Copper corrosion test was carried out according to the method for acopper corrosion test with grease according to JIS K2220. The testtemperature was set at 100° C., and after 24 hours, the condition ofcolor change of a copper plate was observed by the visual test.According to the color change standard for copper plates, the conditionwas evaluated in 4 stages of class 1 to class 4 in which 1 is the best.

The results are shown in Tables 4 to 6. The color of copper plates waslittle changed with the grease compositions in Examples B1 to B12. Incontrast, since Comparative example B1 does not contain a mineral oil orsynthetic oil (that is, since it is a common fluoro grease), the colorchange of copper plates was observed.

Seizure Test:

Each of the grease compositions in Examples B1 to B12 and Comparativeexamples B1 to B6 was filled in a deep groove ball bearing with an ironshield having an inside diameter of 8 mm, an outside diameter of 22 mmand a width of 7 mm (having almost the same structure of the ballbearing of FIG. 8 with the exception that it comprises an iron shieldinstead of contact seals) at 50% the volume of the space portion of theball bearing. Thereafter, the ball bearing was mounted to a tester whichwas similar to the bearing life tester of ASTM D 1741 shown in FIG. 9.

Thereafter, the ball bearing was rotated at a rotational speed of 3,000min⁻¹ under conditions of a bearing temperature of 180° C. and an axialload of 59 N (other conditions were set in accordance with ASTM D 1741.)The life was defined as a time when seizure generated and thetemperature of the outer ring was risen to 190° C. or higher. When thetemperature was not risen to 190° C. or higher even after rotation for1,000 hours, it was evaluated as satisfactory and the test wasterminated. In this rotation test, 4 bearings were used for one type ofbearing, and the mean value was defined as a test result.

The results are shown in Tables 4 to 6. The grease compositions inExamples B1 to B12 had good life. In contrast, since Comparative exampleB2 did not contain a fluoro resin and a PFPE oil (that is, since it is acommon N-substituted terephthalamic acid metal salt grease), theanti-seizuring ability at a high temperature of this grease compositionwas poor. Moreover, since the contents of the fluoro resin and the PFPEoil were small in Comparative examples B4 and B5, the anti-seizuringability at a high temperature of these grease compositions wasinsufficient.

Grease Leakage Test:

Each of the grease compositions in Examples B1 to B12 and Comparativeexamples B1 to B6 was filled in a deep groove ball bearing with rubberseals having an inside diameter of 17 mm, an outside diameter of 40 mmand a width of 12 mm (having the same configuration as the ball bearingof FIG. 8), at 35% the volume of the space portion of the ball bearing.Then, the inner ring was rotated at a rotational speed of 14,500 min⁻¹for 20 hours under conditions of an outer ring temperature of 180° C.and an axial load of 200 N, the mass of the grease composition leakedfrom the bearing during rotation was measured.

When the amount of grease leaked was 10% or less by mass based on thetotal mass of the filled grease composition, it was evaluated assatisfactory. In this test, 4 bearings were used for one type ofbearing, and the mean value was defined as a test result.

The test results are shown in Tables 4 to 6. The leaked amount of eachof the grease compositions in Examples B1 to B12 was small, andtherefore all these grease compositions were evaluated as satisfactory.

FIG. 10 and FIG. 11 are graphs showing the results of the rustprotection test, seizure test and grease leakage test, which werecarried out on the grease compositions in Examples B7 to B12 andComparative examples B1, B2, B4 and B5. The horizontal axis of eachgraph represents the ratio of the fluoro resin (PTFE or a copolymer) inthe thickener.

As is clear from these graphs, when the ratio of the fluoro resin in thethickener was 40 to 80% by mass (that is, the ratio of the N-substitutedterephthalamic acid metal salt being 60 to 20% by mass), both the rustprotection and the seizuring life were excellent, and the amount ofgrease leaked was small.

(C) Grease Composition Comprising Fluoro Resin and Organic Bentonite asThickener

A grease composition comprising a fluoro resin (PTFE) and organicbentonite as thickener was produced. When the fluoro resin is used as athickener, it is desired to use a fluoro oil such as aperfluoropolyether oil (PFPE oil) as a base oil. A mixed base oil of abase oil other than a fluoro oil and the fluoro oil was used, and themixing ratio is preferably a mass ratio which depends on the mass ratiobetween the fluoro resin and the organic bentonite.

The compositions of the grease compositions are as shown in Tables 7 and8. It should be noted that the each value described in the column of“Type of thickeners” in Tables 7 and 8 is the mass ratio of eachcomponent which constitutes the thickener, when the total mass of thethickener is defined as 100. Each value described in the column of “Typeof base oils” has the same meaning. Moreover, values described in thecolumns of “Content of thickeners,” “Content of base oils,” and “Contentof additives” are the mass ratio of each of thickeners, base oils andadditives, in a case where the total mass of the grease composition isdefined as 100. TABLE 7 Example C1 Example C2 Example C3 Example C4 Typeof thickener¹⁾ Organic bentonite 50 80 30 10 PTFE 50 20 70 90 Content ofthickener¹⁾ 25 21 29 33 Type of base Paraffin mineral oil 50 — — 10oils¹⁾ PAO oil²⁾ — 80 — — PETE oil³⁾ — — 30 — Fluoro oil 50 20 70 90Content of base oil¹⁾ 71.5 75.5 67.5 63.5 Content of Naphtylamine⁴⁾ 1 11 1 additive¹⁾ Calcium sulfonate 0.5 0.5 0.5 0.5 Sodium nitrite 2 2 2 2Worked penetration 345 322 355 376 Water washout resistance (% by mass)−1.2 −1.3 −1.0 −0.9 Rust protection property ∘ ∘ ∘ ∘ Seizure load (N)1333 1333 1333 1333 Lubricating life 1.6 2.2 2.3 1.8¹⁾Unit is % by mass²⁾Poly α-olefin oil³⁾Pentaerythritol tetraester oil⁴⁾Phenyl-α-naphthylamine

TABLE 8 Comparative Comparative Comparative Comparative example exampleexample example C1 C2 C3 C4 Type of thickener¹⁾ Organic bentonite 100 —— — PTFE. — 100 — — Content of thickener¹⁾ 18 35 — — Type of base oils¹⁾Paraffin mineral oil 35 — — — PAO oil²⁾ 65 — — — PETE oil³⁾ — — — —Fluoro oil — 100 — — Content of base oil¹⁾ 80.5 63 — — Content ofNaphtylamine⁴⁾ 1 — — — additive¹⁾ Calcium sulfonate 0.5 — — — Sodiumnitrite — 2 — — Worked penetration 312 290 271 285 Water washoutresistance (% by mass) −3.7 −0.6 −0.7 −0.7 Rust protection property x ∘∘ x Seizure load (N) 980 980 980 980 Lubricating life 1.0 2.5 1.6 1.9¹⁾Unit is % by mass²⁾Poly α-olefin oil³⁾Pentaerythritol tetraester oil⁴⁾Phenyl-α-naphthylamine

A method of producing a grease composition comprising a fluoro resin asa thickener is not particularly limited, but a preferred exampleincludes the method described in Japanese Patent Laid-Open No.10-273684. The grease compositions in Comparative examples C1 and C2 arecommercially available fluoro grease compositions.

With regard to these 8 types of grease compositions (Examples C1 to C4,and Comparative Examples C1 to C4), worked penetration and water washoutresistance were determined (according to JIS K2220). In order todetermine water washout resistance, a deep groove ball bearing ofbearing designation 6204 was filled with 4 g of each type of greasecomposition, and the bearing was rotated at 600 min⁻¹ while distilledwater with 79° C. was sprayed thereon at a rate of 5 ml/s. Afterrotation for 1 hour, the reduced amount (% by mass) of the greasecomposition was defined as water washout resistance. The results areshown in Tables 7 and 8.

Moreover, the rust protection, load carrying capacity and lubricatinglife of these grease compositions were also evaluated (refer to Tables 7and 8 for the results). The evaluation methods will be explained below.

Rust Protection Test:

Each of the grease compositions in Examples C1 to C4 and Comparativeexamples C1 to C4 was filled in a deep groove ball bearing with rubberseals having an inside diameter of 17 mm, an outside diameter of 47 mmand a width of 14 mm (not shown) at 50% the volume of the space portionof the ball bearing.

After a running-in (rotation) at a rotational speed of 1,800 min⁻¹ for30 seconds, 0.5 ml of salt water having a concentration of 0.5% by masswas poured in the inside of the bearing, and another running-in wascarried out again at a rotational speed of 1,800 min⁻¹ for 30 seconds.Then, this ball bearing was left at rest for 48 hours in a constanttemperature and humidity bath which was controlled at 80° C. and 100%RH, and thereafter, the ball bearing was decomposed and the condition ofrust generated on the raceway surface was observed by the visual test.The rust condition was evaluated in the following ranks.

-   #7: Generation of no rust-   #6: Generation of very slight rust stain-   #5: Generation of punctated rust with a diameter of 0.3 mm or    shorter-   #4: Generation of rust with a diameter of 1.0 mm or shorter-   #3: Generation of rust with a diameter of 5.0 mm or shorter-   #2: Generation of rust with a diameter of 10.0 mm or shorter-   #1: Generation of rust on almost the entire surface of the raceway    surface

Herein, #7 to #5 were defined as good rust protection, and #4 to #1 weredefined insufficient rust protection. In a graph described later, rustprotection is represented by each of the above values, but in eachtable, good rust protection is represented by the symbol ◯, andinsufficient rust protection is represented by the symbol x.

Evaluation Method of Load Carrying Capacity:

Load carrying capacity was evaluated by a four-ball test, using afour-ball tester based on ASTM. That is, 3 test balls (SUJ2 (thecorresponding US Industrial Standard number SAE52100) steel balls forball bearings having a diameter of about a half inch) were disposed andfixed in a regular triangle form so that the balls were contact with oneanother, and a test ball was then placed and held on a hollow, which wasformed in the center of the three balls.

An evaluation target, grease composition was applied on all the testballs, and the test ball which was placed and held as above was rotatedat a certain rotational speed (4,000 min⁻¹) under load conditions. Theabove load was set at 98 N for 1 minute in the initial rotation stage,and then the load was gradually increased at a rate of 392 N per minute.Seizure load was defined as a load at the time when rotation torque wassharply increased, and load carrying capacity was evaluated with thisseizure load.

Evaluation Method of Lubricating Life:

Each 5 g of the above 8 types of grease compositions was enclosed in arolling bearing separately, and the rolling bearing was then mounted toa tester which was similar to the bearing life tester of ASTM D 1741shown in FIG. 9. Thereafter, the rolling bearing was rotated at arotational speed of 1,000 min⁻¹ under conditions of a temperature of150° C., a radial load of 98 N and an axial load of 294 N. Lubricatinglife was defined as a time when the motor stopped due to overload or atime when the temperature of the bearing exceeded 160° C.

This lubricating life is an L₅₀ life, which was obtained by examining 10tests per one type of bearing and then using a Weibull distributioncurve. The term “lubricating life” is not used herein to mean therolling fatigue life of a bearing due to the generation of flaking, butthe term is used herein to mean the life of a grease determined when abearing becomes not to rotate because of the deterioration of a greasecomposition or the like.

The configuration of the rolling bearing used in the test will beexplained below, while referring to a partial longitudinal sectionalview in FIG. 1.

This rolling bearing (bearing designation 6306VV, inside diameter: 30mm, outside diameter: 72 mm, width: 19 mm) is comprised of: an innerring 1; an outer ring 2; a plurality of balls 3, which are disposedbetween the inner ring 1 and the outer ring 2 so as to flexibly rolltherebetween; a cage 4 for retaining the plurality of balls 3 betweenthe inner ring 1 and the outer ring 2; and noncontact rubber seals 5, 5.

The rubber seal 5 is attached to a seal groove 2 a of the outer ring 2,and the seal covers almost the entire opening portion located betweenthe outer surface of the inner ring 1 and the inner surface of the outerring 2. A space portion, which is formed between the inner ring 1 andthe outer ring 2 and in which the balls 3 were placed, is filled with agrease composition G, and the rubber seals 5, 5 hermetically seal thegrease composition in the bearing. This rubber seal 5 may also be acontact type.

The test results are shown in Tables 7 and 8. The lubricating life isrepresented by a relative value in a case where the lubricating life ofthe grease composition in Comparative example C1 is defined as 1.

As understood from Tables 7 and 8, the grease compositions in ExamplesC1 to C4 were more excellent than the grease compositions in ComparativeExamples C1 to C4 in terms of water washout resistance(water-resisting), rust protection and load carrying capacity(extreme-pressure property). These grease compositions were excellentalso in lubricating life, and the bearing was long-lived underhigh-temperature conditions.

Next, grease compositions were prepared by diversely changing the ratioof organic bentonite to the total mass of the thickener in the greasecomposition of Example C1. Then, rust protection and lubricating lifewere evaluated by the same method as described above. The results areshown in the graph of FIG. 12. The lubricating life in the graph isrepresented by a relative value in a case where the lubricating life ofthe grease composition in Comparative example C1 is defined as 1. Thegraph shows that when the content of the organic bentonite is 10 to 90%by mass, the rust protection and the lubricating life are excellent.

Moreover, grease compositions were prepared by diversely changing thecontent of thickener to the total mass of the grease composition in thegrease composition of Example C1. Then, lubricating life was evaluatedby the same method as described above. The results are shown in thegraph of FIG. 13. The lubricating life in the graph is represented by arelative value in a case where the lubricating life of the greasecomposition in Comparative example C1 is defined as 1.

This graph shows that when the content of the thickener is 5 to 38% bymass based on the total mass of the grease composition, the lubricatinglife of the grease composition is excellent. The graph also shows that,when the content is 8 to 30% by mass, the lubricating life is moreexcellent, and when the content is 12 to 23% by mass, the lubricatinglife is further more excellent.

(D) Grease Composition Comprising Fluoro Resin and Calcium SulfonateComplex as Thickener

The configuration of a rolling bearing filled with a grease compositioncomprising a fluoro resin and a calcium sulfonate complex as thickenersis not particularly limited, but an example includes the ball bearingshown in FIG. 14. The ball bearing 201, as illustrated in the figure, iscomprised of an inner ring 210; an outer ring 211; a plurality of balls213, which are disposed between the inner ring 210 and the outer ring211 so as to flexibly roll therebetween; and a cage 212 for retainingthe plurality of balls 213, wherein the space portion of the bearing Sis filled with a grease composition described later, and a seal 214seals the grease composition in the bearing.

The present invention is further described in the following examples andcomparative examples. However, these examples are not intended to limitthe scope of the invention.

Using base oils and thickeners as shown in Table 9, ten types of greasecompositions (Examples D1 to D6 and Comparative examples D1 to D4) wereprepared. The content of the thicker was set at 30% by mass in any ofthe grease compositions. Using these 10 types of grease compositions,each of the following tests was carried out. The results are shown inTable 9. TABLE 9 Comparative Comparative Comparative Comparative ExampleExample Example Example Example Example example example example exampleD1 D2 D3 D4 D5 D6 D1 D2 D3 D4 Thickener A 50 20 5 50 80 95 100 — 3 97(mass ratio) Thickener B 50 80 95 50 20 5 — 100 97 3 (mass ratio) Baseoil A ADE(50) PET(20) DPET(5) ADE DPET + PAO MO — PET(3) PAO(97) (massratio) MO Base oil B PFPE(50) PFPE(80) PFPE(95) — — — — PFPE PFPE(97)PFPE(3) (mass ratio) Seizure 1500 1280 1100 1580 1780 1700 1820 10001000 1650 load (N) Lubricating 1780 1880 2000 1580 1540 1620 1280 21802020 1420 life (hr) Result of rust ∘ ∘ ∘ ∘ ∘ ∘ ∘ x Δ ∘ protection testThickener A: Calcium sulfonate complexThickener B: PolytetrafluoroethylenePFPE: PerfluoropolyetherADE: AlkyldiphenyletherPET: Pentaerythritol esterDPET: Dipentaerythritol esterPAO: Poly α-olefinMO: Mineral oilEvaluation Method of Load Carrying Capacity:

Load carrying capacity was evaluated by a four-ball test, using afour-ball tester based on ASTM, in the same manner as described above.That is, 3 test balls (SUJ2 (the corresponding US Industrial Standardnumber SAE52100) steel balls for ball bearings having a diameter ofabout a half inch) were disposed and fixed in a regular triangle form sothat the balls were contact with one another, and a test ball was thenplaced and held on a hollow, which was formed in the center of the threeballs.

Thereafter, an evaluation target, grease composition was applied on allthe test balls, and the test ball which was placed and held as above wasrotated at a certain rotational speed (4,000 min⁻¹) under loadconditions. The above load was gradually increased at a rate of 1,800 Nper minute. Seizure load was defined as a load at the time when rotationtorque was sharply increased. Load carrying capacity was evaluated withthis seizure load, and when the seizure load was 1,100 N or more, thegrease composition was evaluated as satisfactory.

Evaluation Method of Lubricating Life:

Lubricating life was evaluated, using a tester similar to the bearinglife tester of ASTM D 1741 shown in FIG. 9.

First, the space portion of a rolling bearing (bearing designation6306VV) manufactured by NSK Ltd., was filled with a grease compositionat 35% the volume of the space portion. Thereafter, the rolling bearingwas mounted to the above tester, and the inner ring was then rotated ata rotational speed of 7,000 min⁻¹ under conditions of a temperature of180° C., a radial load of 98 N and an axial load of 294 N. A cycle ofrotating the inner ring for 24 hours and then stopping it for 4 hourswas repeated. Lubricating life was defined as a time when the motorstopped due to overload or a time when the temperature of the bearingexceeded 190° C.

When the lubricating life was 1,500 hours or longer, the greasecomposition was evaluated as satisfactory.

Rust Protection Test:

The space portion of a rolling bearing (bearing designation 6202VV)manufactured by NSK Ltd., was filled with each of the greasecompositions in Examples D1 to D6 and Comparative examples D1 to D4 at35% the volume of the space portion.

Thereafter, under load conditions of an axial preload of 39.2 N, therolling bearing was left for 1 month in a constant temperature andhumidity bath, which was controlled at 80° C. and at 90% RH. At thattime, the rolling bearing was placed in the constant temperature andhumidity bath at an ordinary temperature without preheating it, so as tocause condensation on the rolling bearing. One month later, the rollingbearing was taken out of the constant temperature and humidity bath. Therolling bearing was then decomposed, and the condition of rust generatedwas visually observed. Rust protection was evaluated according to thefollowing standard:

-   No rust: ◯ (Satisfactory)-   Punctated rust (1 to 3 spots): Δ (Unsatisfactory)-   Punctated rust (many spots): x (Unsatisfactory)

As shown in Table 9, the rolling bearing of each Example filled with agrease composition which comprises, as a thickener, a calcium sulfonatecomplex consisting of calcium sulfonate and a calcium salt and a fluororesin had a seizuring load which further exceeded 1,100 N as asatisfactory standard. Moreover, the rolling bearing of each Example hada lubricating life which further exceeded 1,500 hours as a satisfactorystandard. Furthermore, in all the Examples, the rolling bearing passedthe rust protection test.

In contrast, the lubricating life of the rolling bearing of Comparativeexample D1 did not reach the satisfactory standard. Moreover, the loadcarrying capacity and the rust protection of the rolling bearings ofComparative examples D2 and D3 did not reach the satisfactory standard.Furthermore, the lubricating life of the rolling bearing of Comparativeexample D4 did not reach the satisfactory standard.

(E) Grease Composition Comprising Fluoro Resin and Carbon Black asThickener

FIG. 15 is a partial longitudinal sectional view showing theconfiguration of a ball bearing 321, which is one embodiment of therolling apparatus of the present invention. This ball bearing 321 iscomprised of: an outer ring 322; an inner ring 323; a plurality of balls324, which are disposed between the outer ring 322 and the inner ring323 so as to flexibly roll therebetween; a cage 325 for retaining theplurality of balls 324; and noncontact seals 326, 326 installed in theseal groove 322 b of the outer ring 322. A space portion, which issurrounded by the outer ring 322, the inner ring 323 and the seals 326,326 are filled with a grease composition 327, and the seal 326hermetically sealed the grease composition 327 in the ball bearing 321.

This grease composition 327 comprises 20% by mass of a thickener and 80%by mass of a base oil. The thickener comprises 50% by mass of carbonblack and 50% by mass of PTFE, and the base oil comprises 50% by mass ofa poly α-olefin oil and 50% by mass of a perfluoropolyether oil (PFPEoil).

Since the grease composition 327 comprises carbon black, the greasecomposition 327 lubricates the contact surface between the racewaysurfaces 322 a and 323 a of the above both rings 322 and 323, and theballs 324, and also conducts electricity to the outer ring 322, theinner ring 323 and the balls 324. In addition, the outer ring 322 orinner ring 323 is grounded (not shown in the figure), so that staticelectricity generated by the rotation of the ball bearing 321 can beeliminated. If the seal 326 is a contact type seal and is made fromconductive rubber so that also the seal 326 obtains electricconductivity, the electric conductivity of the ball bearing 321 can bebetter.

Since the grease composition 327 comprises PTFE and a PFPE oil, thisgrease composition has excellent heat resistance.

A rolling apparatus such as a ball bearing filled with this greasecomposition has excellent electric conductivity and is long-lived underhigh temperature conditions, and therefore it can preferably be used asa rolling or sliding portion of machines used under high-temperature andhigh-speed conditions including car electrical components such asalternators or electromagnetic clutches; auxiliary equipment for carengine such as idler pulleys; and business machines such as copyingmachines or printers.

Next, with regard to 16 types of grease compositions (Examples E1 toE10, and Comparative Examples E1 to E6) which have almost the samecomposition as the above described grease composition 327, a workedpenetration determination, a rust protection test, a copper corrosiontest, a seizure test and an electric conductivity test were carried out.

The compositions of the grease compositions of Examples E1 to E10 andComparative examples E1 to E6 are as shown in Tables 10 to 12, and eachgrease composition comprises a thickener consisting of carbon black anda fluoro resin (PTFE or a copolymer) and a base oil consisting of asynthetic oil and a PFPE oil (except Comparative examples E1 and E2).Each grease composition further comprises, as additives, 1.0% by mass ofan amine antioxidant, 0.5% by mass of a calcium sulfonate rustpreventive and 0.05% by mass of a benzotriazole metal deactivator basedon the total mass of the grease composition. TABLE 10 Example ExampleExample Example Example E1 E2 E3 E4 E5 Type of thickener¹⁾ Carbon black50 60 20 50 60 PTFE 50 40 80 — — Copolymer²⁾ — — — 50 40 Content ofthickener¹⁾ 20 18 28 20 18 Type of base oils¹⁾ PAO oil³⁾ 50 73 21 50 52ADPE oil⁴⁾ — — — — — PFPE oil 50 27 79 50 48 Content of base oil¹⁾ 80 8272 80 82 Worked penetration 278 280 270 273 272 Copper corrosion test 11 1 1 1 Rust protection test #6 #6 #5 #6 #6 Seizure test (for life) 1.91.9 2.3 2.0 1.8 Electric conductivity test (for 0.09 0.08 0.18 0.10 0.08bearing's resistance)¹⁾Unit is % by mass²⁾Copolymer of vinylidene fluoride and hexafluoroisobutylene (molarratio 1:1)³⁾Poly α-olefin oil⁴⁾Alkyldiphenylether oil

TABLE 11 Example Example Example Example Example E6 E7 E8 E9 E10 Type ofthickener¹⁾ Carbon black 50 30 20 50 60 PTFE 50 70 80 — — Copolymer²⁾ —— — 50 40 Content of thickener¹⁾ 20 28 28 20 20 Type of base oils¹⁾ PAOoil³⁾ — — — — — ADPE oil⁴⁾ 38 28 20 50 50 PFPE oil 62 72 80 50 50Content of base oil¹⁾ 80 72 72 80 80 Worked penetration 268 264 270 276265 Copper corrosion test 1 1 1 1 1 Rust protection test #6 #5 #5 #6 #6Seizure test (for life) 2.5 2.6 2.6 2.4 2.4 Electric conductivity test(for 0.13 0.24 0.25 0.15 0.10 bearing's resistance)¹⁾Unit is % by mass²⁾Copolymer of vinylidene fluoride and hexafluoroisobutylene (molarratio 1:1)³⁾Poly α-olefin oil⁴⁾Alkyldiphenylether oil

TABLE 12 Comparative Comparative Comparative Comparative ComparativeComparative example E1 example E2 example E3 example E4 example E5example E6 Type of thickener¹⁾ Carbon black — 100 50 80 70 50 PTFE 100 —50 — — — Copolymer²⁾ — — — 20 30 50 Content of thickener¹⁾ 35 10 3 20 2342 Type of base oils¹⁾ PAO oil³⁾ — — — — — — ADPE oil⁴⁾ — 100 48 75 6583 PFPE oil 100 — 52 25 35 17 Content of base oil¹⁾ 65 90 97 80 77 58Worked penetration 293 267 — 271 272 190 Copper corrosion test 4 1 — 1 11 Rust protection test #1 #7 — #6 #6 #6 Seizure test (for life) 2.8 1 —1.2 1.3 1.2 Electric conductivity test (for 1.00 0.05 — 0.07 0.07 0.10bearing's resistance)¹⁾Unit is % by mass²⁾Copolymer of vinylidene fluoride and hexafluoroisobutylene (molarratio 1:1)³⁾Poly α-olefin oil⁴⁾Alkyldiphenylether oil

It should be noted that the content of the base oil and the thickenerdescribed in each of Tables 10 to 12 is a value based on that the totalmass of the base oil and the thickener is defined as 100, and that theabove additives are not considered. Moreover, values described in thecolumns of the type of thickener and the type of base oil show the massratio (% by mass) of each component based on the total mass of thethickener and the total mass of the base oil.

Each component of the grease composition will be explained below.

-   -   Carbon black: a primary particle size of 30 nm, a DBP oil        absorption with a dibutyl phthalate absorptiometer of 350 ml/100        g, and a specific surface area by nitrogen adsorption of 800        m²/g    -   Copolymer: a copolymer of vinylidene fluoride and        hexafluoroisobutylene (mole ratio being 1:1)    -   Poly α-olefin oil: a kinematic viscosity at 40° C. being 60        mm²/s    -   Alkyl diphenyl ether oil: a kinematic viscosity at 40° C. being        100 mm²/s    -   PFPE oil: a kinematic viscosity at 40° C. being 190 mm²/s

Next, each test method and test results will be explained below.

Worked Penetration Determination:

Worked penetration was determined according to JIS K2220.

The results are shown in Tables 10 to 12. The grease compositions inExamples E1 to E10 had good worked penetration. In contrast, since thecontent of the thickener was too large in Comparative example E6, theworked penetration was small. Moreover, since the content of thethickener is too small in Comparative example E3, the grease compositiondid not become a grease state.

Rust Protection Test:

Each of the grease compositions in Examples E1 to E10 and Comparativeexamples E1 to E6 was filled in a deep groove ball bearing with rubberseals having an inside diameter of 17 mm, an outside diameter of 47 mmand a width of 14 mm (having almost the same configuration as the ballbearing of FIG. 8,) at 50% the volume of the space portion of the ballbearing.

After a running-in (rotation) at a rotational speed of 1,800 min⁻¹ for30 seconds, 0.5 ml of 0.5% by mass of salt water was poured in theinside of the bearing, and another running-in was carried out again at arotational speed of 1,800 min⁻¹ for 30 seconds. Then, this ball bearingwas left at rest for 48 hours in a constant temperature and humiditybath which was controlled at 80° C. and 100% RH, and thereafter, theball bearing was decomposed and the condition of rust generated on theraceway surface was observed by the visual test. The rust condition wasevaluated in the following ranks:

-   #7: Generation of no rust-   #6: Generation of very slight rust stain-   #5: Generation of punctated rust with a diameter of 0.3 mm or    shorter-   #4: Generation of rust with a diameter of 1.0 mm or shorter-   #3: Generation of rust with a diameter of 5.0 mm or shorter-   #2: Generation of rust with a diameter of 10.0 mm or shorter-   #1: Generation of rust on almost the entire surface of the raceway    surface

Herein, #7 to #5 were defined as good rust protection, and #4 to #1 weredefined insufficient rust protection.

The results are shown in Tables 10 to 12. The grease compositions inExamples E1 to E10 showed good rust protection. In contrast, sinceComparative example E1 did not contain a mineral oil or synthetic oil(that is, since it is a common fluoro grease), the rust protection wasinsufficient.

Copper Corrosion Test:

Copper corrosion test was carried out according to the method for acopper corrosion test with grease according to JIS K2220. The testtemperature was set at 100° C., and after 24 hours, the condition ofcolor change of a copper plate was observed by the visual test.According to the color change standard for copper plates, the conditionwas evaluated in 4 stages of class 1 to class 4 in which 1 is the best.

The results are shown in Tables 10 to 12. The color of copper plates waslittle changed with the grease compositions in Examples E1 to E10. Incontrast, since Comparative example E1 did not contain a mineral oil orsynthetic oil (that is, since it is a common fluoro grease), the colorchange of copper plates was observed.

Seizure Test:

Each of the grease compositions in Examples E1 to E10 and Comparativeexamples E1 to E6 was filled in a deep groove ball bearing with an ironshield having an inside diameter of 8 mm, an outside diameter of 22 mmand a width of 7 mm (having the same configuration of the ball bearingof FIG. 15) at 50% the volume of the space portion of the ball bearing.Thereafter, the ball bearing was mounted to a tester which was similarto the bearing life tester of ASTM D 1741 shown in FIG. 9.

Thereafter, the ball bearing was rotated at a rotational speed of 3,000min⁻¹ under conditions of a bearing temperature of 180° C. and an axialload of 59 N (other conditions were set in accordance with ASTM D 1741.)The life was defined as a time when seizure generated and thetemperature of the outer ring was risen to 190° C. or higher. When thetemperature was not risen to 190° C. or higher even after rotation for1,000 hours, it was evaluated as satisfactory and the test wasterminated. In this rotation test, 4 bearings were used for one type ofbearing, and the mean value was defined as a test result.

The results are shown in Tables 10 to 12. The life described in each ofTables 10 to 12 is a relative value in a case where the life ofComparative example E2 is defined as 1. The grease compositions inExamples E1 to E10 had good life. In contrast, since Comparative exampleE2 did not contain a fluoro resin and a PFPE oil (that is, since it is acommon carbon black grease), the anti-seizuring ability at a hightemperature was poor. Moreover, since the contents of the fluoro resinand the PFPE oil were small in Comparative examples E4 and E5, theanti-seizuring ability at a high temperature of these greasecompositions was insufficient.

Electric Conductivity Test:

Each of the grease compositions in Examples E1 to E10 and Comparativeexamples E1 to E6 were filled in a ball bearing having the sameconfiguration as in FIG. 15 at 50% the volume of the space portion ofthe bearing, and the ball bearing was then mounted to an apparatus shownin FIG. 16. Thereafter, electric resistance (maximum) between the innerring and the outer ring during rotation was measured. The ball bearingwas first rotated for 100 hours under the conditions of the aboveseizure test, and it was then subjected to this electric conductivitytest.

First, the apparatus for measuring resistance will be explained,referring to the schematic block diagram of FIG. 16.

In FIG. 16, a numerical code 401 denotes a ball bearing that is ameasurement target, and the apparatus is configured that a motor 403rotates a shaft 402 installed in the inner ring 401 a, so that the ballbearing 401 rotates. A certain constant voltage is applied between theshaft 402 installed in the inner ring 401 a and an outer ring 401 b by aconstant-voltage power supply 404. An electric resistance measuringdevice 405 is connected in parallel to the constant-voltage power supply404.

The electric resistance measuring device 405 outputs a measured voltagevalue (an analog value) to an A/D conversion circuit 406. The A/Dconversion circuit 406 converts the measured voltage value to a digitalvalue based on a previously established sampling cycle, and then itoutputs the converted digital signal to a processor 407. In the presentembodiment, the sampling cycle is set at 50 kHz (sampling timeinterval=0.02 ms).

The processor 407 is comprised of a maximum resistance processing unit407A, a threshold processing unit 407B, and a wave number counting unit407C. The maximum resistance processing unit 407A calculates the maximumresistance based on the input digital signal. The threshold processingunit 407B processes the input digital signal with a certain thresholdvalue so as to eliminate noise. The wave number counting unit 407Ccounts the fluctuation number per certain time unit, that is, the wavenumber of waves regarding pulse counts from the threshold processingunit 407B, based on the fluctuation of pulse values over time, and thenthe unit 407C obtains the mean value of wave numbers per unit time. Theprocessor 407 outputs the obtained maximum resistance and the mean valueof wave numbers per unit time to a displaying device 408. In the presentembodiment, the unit time for counting the above wave number is set at0.328 second. The displaying device 408 is comprised of a display andothers, and it displays the maximum resistance and the mean value ofwave numbers per unit time obtained by the processor 407.

Next, a method of evaluating the electric resistance of the ball bearing401 using the above configured apparatus will be explained.

Under the conditions where the shaft 402, that is, the inner ring 401 ais being rotated at a certain rotational speed by the motor 403, acertain constant voltage is applied between the inner ring 401 a and theouter ring 401 b of the bearing 401 by the constant-voltage power supply404. At this time, an electric current is passed between the inner ring401 a and the outer ring 401 b, but the voltage is fluctuated by sparkor the like. The voltage is measured by the resistance measuringapparatus 405, the measured value is then converted into a digital valueby the A/D conversion circuit 406, and based on the digital signal, themaximum resistance and the wave number per certain unit time areobtained by the processor 407, and finally the obtained values aredisplayed on the displaying device 408.

The measurement conditions are as follows:

-   -   Inner ring rotational speed: 100 min⁻¹    -   Radial load (Fr) applied on bearing 401: 19.6 N    -   Voltage applied: 6.2 V    -   Maximum electric current: 100 μA    -   Series resistance: 62 kΩ    -   Atmosphere temperature: 40° C.    -   Atmosphere humidity: 50% RH

The results are shown in Tables 10 to 12. It should be noted that thebearing electric resistances described in Tables 10 to 12 are relativevalues in a case where the bearing electric resistance of Comparativeexample E1 is defined as 1.

The grease compositions in Examples E1 to E10 had good electricconductivity, but the grease composition in Comparative example E1 hadpoor electric conductivity because it did not contain carbon black.

FIGS. 17 and 18 are graphs showing the results of the rust protectiontest, the seizure test and the electric conductivity test of the greasecompositions of Examples E6 to E10 and Comparative examples E1, E2, E4and E5. The horizontal axis of each graph represents the ratio of thefluoro resin (PTFE or a copolymer) in the thickener.

As is shown in these graphs, when the ratio of the fluoro resin in thethickener is 40 to 80% by mass (that is, the ratio of carbon black being60 to 20% by mass), the grease composition is excellent in all of therust protection, the seizuring life and the electric conductivity.

These embodiments are provided for illustrative purposes only, and arenot intended to limit the scope of the invention.

For example, the types of the base oils, thickeners and additives usedin the present grease composition are not limited to the above describedones.

Further, in the present embodiments, a deep groove ball bearing was usedto explain the rolling apparatus of the present invention. However, thepresent invention can be applied to other various types of rollingbearings. Examples of such rolling bearings include radial rollingbearings such as an angular contact ball bearing, a self-aligning ballbearing, a cylindrical roller bearing, a tapered roller bearing, aneedle roller bearing and a self-aligning roller bearing, and thrustrolling bearings such as a thrust ball bearing and a thrust rollerbearing.

Moreover, the present invention is not limited to a rolling bearing, butcan be applied to other various types of rolling apparatus. Examples ofsuch rolling apparatuses include a ball screw, a linear guide apparatus,a linear bearing and others.

1. A grease composition comprising a base oil and a thickener, whereinsaid thickener comprises a fluoro resin and a second thickenercomponent, wherein said second thickener component is an N-substitutedterephthalamic acid metal salt.
 2. The grease composition according toclaim 1, wherein said thickener comprises 40 to 80% by mass of thefluoro resin and 60 to 20% by mass of the N-substituted terephthalamicacid metal salt.
 3. The grease composition according to claim 2, whereinthe content of said thickener is 5 to 40% by mass based on the totalmass of the composition.
 4. The grease composition according to claim 2,wherein said base oil comprises a perfluoropolyether oil and at leastone of either a mineral oil or synthetic oil.
 5. The grease compositionaccording to claim 4, wherein said base oil comprises 10 to 90% by massof the perfluoropolyether oil and 90 to 10% by mass of at least one ofeither the mineral oil or synthetic oil.
 6. The grease compositionaccording to claim 5, wherein said perfluoropolyether oil has akinematic viscosity at 40° C. of 20 to 400 mm²/s, and at least one ofeither said mineral oil or synthetic oil has a kinematic viscosity at40° C. of 20 to 400 mm²/s.
 7. The grease composition according to claim2, which comprises an additive, wherein the content of said additive is20% or less by mass based on the total mass of the composition.
 8. Arolling apparatus comprising an inner member having a raceway surface onthe outer surface; an outer member which has a raceway surface opposedto the raceway surface of said inner member and is disposed outside ofsaid inner member; and a plurality of rolling elements which aredisposed between said two raceway surfaces so as to flexibly rolltherebetween, wherein a space, which is formed between said inner memberand said outer member and in which said rolling elements are disposed,is filled with the grease composition according to claim
 1. 9. Therolling apparatus according to claim 8, which is a rolling bearing usedfor car electrical components, auxiliary equipment for car engine orbusiness machines used under high-speed and/or high-temperatureenvironment.